diff --git a/app/build.gradle b/app/build.gradle
index c8b4b59..95fa2e3 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -1,13 +1,13 @@
 apply plugin: 'com.android.application'
+apply plugin: 'org.jetbrains.kotlin.android'
 
 android {
-    compileSdk 26
+    compileSdk 34
 
     defaultConfig {
         applicationId "de.rochefort.childmonitor"
         minSdkVersion 21
-        //noinspection ExpiredTargetSdkVersion
-        targetSdkVersion 26
+        targetSdkVersion 34
         versionCode 11
         versionName "1.1"
     }
@@ -19,9 +19,7 @@ android {
         }
     }
 
-
     dependencies {
-        implementation "com.android.support:support-compat:26.1.0"
     }
     namespace 'de.rochefort.childmonitor'
     lint {
@@ -29,7 +27,16 @@ android {
         warning 'MissingTranslation'
     }
     compileOptions {
-        sourceCompatibility JavaVersion.VERSION_1_8
-        targetCompatibility JavaVersion.VERSION_1_8
+        // Sets Java compatibility to Java 17
+        sourceCompatibility JavaVersion.VERSION_17
+        targetCompatibility JavaVersion.VERSION_17
     }
+    kotlin {
+        jvmToolchain(17)
+    }
+}
+
+dependencies {
+    implementation 'androidx.core:core:1.12.0'
+    implementation 'androidx.core:core-ktx:1.12.0'
 }
\ No newline at end of file
diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index 6c0b841..6725f91 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -20,6 +20,10 @@
         android:required="true" />
     <uses-permission
         android:name="android.permission.FOREGROUND_SERVICE"/>
+    <uses-permission
+        android:name="android.permission.FOREGROUND_SERVICE_MEDIA_PLAYBACK"/>
+    <uses-permission
+        android:name="android.permission.FOREGROUND_SERVICE_MICROPHONE"/>
 
     <application
         android:allowBackup="true"
@@ -30,10 +34,12 @@
         <service
             android:name=".ListenService"
             android:enabled="true"
+            android:foregroundServiceType="mediaPlayback"
             android:exported="false"/>
         <service
             android:name=".MonitorService"
             android:enabled="true"
+            android:foregroundServiceType="microphone"
             android:exported="false"/>
 
         <activity
diff --git a/app/src/main/java/de/rochefort/childmonitor/AudioCodecDefines.java b/app/src/main/java/de/rochefort/childmonitor/AudioCodecDefines.kt
similarity index 54%
rename from app/src/main/java/de/rochefort/childmonitor/AudioCodecDefines.java
rename to app/src/main/java/de/rochefort/childmonitor/AudioCodecDefines.kt
index fc801f2..0bfa0a8 100644
--- a/app/src/main/java/de/rochefort/childmonitor/AudioCodecDefines.java
+++ b/app/src/main/java/de/rochefort/childmonitor/AudioCodecDefines.kt
@@ -14,20 +14,21 @@
  * You should have received a copy of the GNU General Public License
  * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
  */
-package de.rochefort.childmonitor;
+package de.rochefort.childmonitor
 
-import android.media.AudioFormat;
+import android.media.AudioFormat
+import de.rochefort.childmonitor.audio.G711UCodec
 
-import de.rochefort.childmonitor.audio.G711UCodec;
+class AudioCodecDefines private constructor() {
+    init {
+        throw IllegalStateException("Do not instantiate!")
+    }
 
-public class AudioCodecDefines {
-    public static final int FREQUENCY = 8000;
-    public static final int ENCODING = AudioFormat.ENCODING_PCM_16BIT;
-    public static final G711UCodec CODEC = new G711UCodec();
-    public static final int CHANNEL_CONFIGURATION_IN = AudioFormat.CHANNEL_IN_MONO;
-    public static final int CHANNEL_CONFIGURATION_OUT = AudioFormat.CHANNEL_OUT_MONO;
-
-    private AudioCodecDefines() {
-        throw new IllegalStateException("Do not instantiate!");
+    companion object {
+        const val FREQUENCY = 8000
+        const val ENCODING = AudioFormat.ENCODING_PCM_16BIT
+        val CODEC = G711UCodec()
+        const val CHANNEL_CONFIGURATION_IN = AudioFormat.CHANNEL_IN_MONO
+        const val CHANNEL_CONFIGURATION_OUT = AudioFormat.CHANNEL_OUT_MONO
     }
 }
diff --git a/app/src/main/java/de/rochefort/childmonitor/DiscoverActivity.java b/app/src/main/java/de/rochefort/childmonitor/DiscoverActivity.java
deleted file mode 100644
index d260cd3..0000000
--- a/app/src/main/java/de/rochefort/childmonitor/DiscoverActivity.java
+++ /dev/null
@@ -1,297 +0,0 @@
-/*
- * This file is part of Child Monitor.
- *
- * Child Monitor is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Child Monitor is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
- */
-package de.rochefort.childmonitor;
-
-import android.app.Activity;
-import android.content.Context;
-import android.content.Intent;
-import android.content.SharedPreferences;
-import android.net.nsd.NsdManager;
-import android.net.nsd.NsdServiceInfo;
-import android.net.wifi.WifiManager;
-import android.os.Bundle;
-import android.util.Log;
-import android.widget.ArrayAdapter;
-import android.widget.Button;
-import android.widget.EditText;
-import android.widget.ListView;
-import android.widget.Toast;
-
-import java.util.Objects;
-
-
-public class DiscoverActivity extends Activity {
-    private static final String PREF_KEY_CHILD_DEVICE_ADDRESS = "childDeviceAddress";
-    private static final String PREF_KEY_CHILD_DEVICE_PORT = "childDevicePort";
-    final String TAG = "ChildMonitor";
-
-    private NsdManager nsdManager;
-
-    private NsdManager.DiscoveryListener discoveryListener;
-
-    @Override
-    protected void onCreate(Bundle savedInstanceState) {
-        Log.i(TAG, "ChildMonitor start");
-
-        nsdManager = (NsdManager)this.getSystemService(Context.NSD_SERVICE);
-
-        super.onCreate(savedInstanceState);
-        setContentView(R.layout.activity_discover);
-
-        final Button discoverChildButton = findViewById(R.id.discoverChildButton);
-        discoverChildButton.setOnClickListener(v -> loadDiscoveryViaMdns());
-
-        final Button enterChildAddressButton = findViewById(R.id.enterChildAddressButton);
-        enterChildAddressButton.setOnClickListener(v -> loadDiscoveryViaAddress());
-    }
-
-    private void loadDiscoveryViaMdns() {
-        setContentView(R.layout.activity_discover_mdns);
-        startServiceDiscovery("_childmonitor._tcp.");
-    }
-
-    private void loadDiscoveryViaAddress() {
-        setContentView(R.layout.activity_discover_address);
-
-        final Button connectButton = findViewById(R.id.connectViaAddressButton);
-        final EditText addressField = findViewById(R.id.ipAddressField);
-        final EditText portField = findViewById(R.id.portField);
-        String preferredAddress = getPreferences(MODE_PRIVATE).getString(PREF_KEY_CHILD_DEVICE_ADDRESS, null);
-        if (preferredAddress != null && !preferredAddress.isEmpty()) {
-            addressField.setText(preferredAddress);
-        }
-        int preferredPort = getPreferences(MODE_PRIVATE).getInt(PREF_KEY_CHILD_DEVICE_PORT, -1);
-        if (preferredPort > 0) {
-            portField.setText(String.valueOf(preferredPort));
-        } else {
-            portField.setText("10000");
-        }
-
-        connectButton.setOnClickListener(v -> {
-            Log.i(TAG, "Connecting to child device via address");
-            final String addressString = addressField.getText().toString();
-            final String portString = portField.getText().toString();
-
-            if(addressString.length() == 0)
-            {
-                Toast.makeText(DiscoverActivity.this, R.string.invalidAddress, Toast.LENGTH_LONG).show();
-                return;
-            }
-
-            int port;
-
-            try {
-                port = Integer.parseInt(portString);
-            }
-            catch(NumberFormatException e)
-            {
-                Toast.makeText(DiscoverActivity.this, R.string.invalidPort, Toast.LENGTH_LONG).show();
-                return;
-            }
-            SharedPreferences.Editor preferencesEditor = getPreferences(MODE_PRIVATE).edit();
-            preferencesEditor.putString(PREF_KEY_CHILD_DEVICE_ADDRESS, addressString);
-            preferencesEditor.putInt(PREF_KEY_CHILD_DEVICE_PORT, port);
-            preferencesEditor.apply();
-            connectToChild(addressString, port, addressString);
-        });
-    }
-
-    @Override
-    protected void onDestroy() {
-        Log.i(TAG, "ChildMonitoring stop");
-
-        if(discoveryListener != null) {
-            Log.i(TAG, "Unregistering monitoring service");
-
-            nsdManager.stopServiceDiscovery(discoveryListener);
-            discoveryListener = null;
-        }
-
-        super.onDestroy();
-    }
-
-    public void startServiceDiscovery(final String serviceType) {
-        final NsdManager nsdManager = (NsdManager)this.getSystemService(Context.NSD_SERVICE);
-        if (nsdManager == null) {
-            Log.e(TAG, "Could not obtain nsdManager");
-            return;
-        }
-
-        WifiManager wifi = (WifiManager) this.getApplicationContext().getSystemService(Context.WIFI_SERVICE);
-        final Runnable multicastReleaser;
-        if (wifi != null) {
-            final WifiManager.MulticastLock multicastLock = wifi.createMulticastLock("multicastLock");
-            multicastLock.setReferenceCounted(true);
-            multicastLock.acquire();
-            multicastReleaser = () -> {
-                try {
-                    multicastLock.release();
-                } catch (Exception ignored) {
-                    //dont really care
-                }
-            };
-        } else {
-            multicastReleaser = () -> {
-            };
-        }
-
-
-        final ListView serviceTable = findViewById(R.id.ServiceTable);
-
-        final ArrayAdapter<ServiceInfoWrapper> availableServicesAdapter = new ArrayAdapter<>(this,
-                R.layout.available_children_list);
-        serviceTable.setAdapter(availableServicesAdapter);
-
-        serviceTable.setOnItemClickListener((parent, view, position, id) -> {
-            final ServiceInfoWrapper info = (ServiceInfoWrapper) parent.getItemAtPosition(position);
-            connectToChild(info.getAddress(), info.getPort(), info.getName());
-        });
-
-        // Instantiate a new DiscoveryListener
-        discoveryListener = new NsdManager.DiscoveryListener() {
-            //  Called as soon as service discovery begins.
-            @Override
-            public void onDiscoveryStarted(String regType)
-            {
-                Log.d(TAG, "Service discovery started");
-            }
-
-            @Override
-            public void onServiceFound(NsdServiceInfo service) {
-                // A service was found!  Do something with it.
-                Log.d(TAG, "Service discovery success: " + service);
-
-                if (!service.getServiceType().equals(serviceType)) {
-                    // Service type is the string containing the protocol and
-                    // transport layer for this service.
-                    Log.d(TAG, "Unknown Service Type: " + service.getServiceType());
-                } else if (service.getServiceName().contains("ChildMonitor")) {
-                    NsdManager.ResolveListener resolver = new NsdManager.ResolveListener() {
-                        @Override
-                        public void onResolveFailed(NsdServiceInfo serviceInfo, int errorCode) {
-                            // Called when the resolve fails.  Use the error code to debug.
-                            Log.e(TAG, "Resolve failed: error " + errorCode + " for service: " + serviceInfo);
-                        }
-
-                        @Override
-                        public void onServiceResolved(final NsdServiceInfo serviceInfo) {
-                            Log.i(TAG, "Resolve Succeeded: " + serviceInfo);
-
-                            DiscoverActivity.this.runOnUiThread(() -> {
-                                for (int index=0; index < availableServicesAdapter.getCount(); index++) {
-                                    ServiceInfoWrapper item = availableServicesAdapter.getItem(index);
-                                    if (item != null && item.matches(serviceInfo)) {
-                                        // Prevent inserting duplicates
-                                        return;
-                                    }
-                                }
-                                availableServicesAdapter.add(new ServiceInfoWrapper(serviceInfo));
-                            });
-                        }
-                    };
-
-                    DiscoverActivity.this.nsdManager.resolveService(service, resolver);
-                } else {
-                    Log.d(TAG, "Unknown Service name: " + service.getServiceName());
-                }
-            }
-
-            @Override
-            public void onServiceLost(NsdServiceInfo service) {
-                // When the network service is no longer available.
-                // Internal bookkeeping code goes here.
-                Log.e(TAG, "Service lost: " + service);
-                multicastReleaser.run();
-            }
-
-            @Override
-            public void onDiscoveryStopped(String serviceType) {
-                Log.i(TAG, "Discovery stopped: " + serviceType);
-                multicastReleaser.run();
-            }
-
-            @Override
-            public void onStartDiscoveryFailed(String serviceType, int errorCode) {
-                Log.e(TAG, "Discovery failed: Error code: " + errorCode);
-                nsdManager.stopServiceDiscovery(this);
-                multicastReleaser.run();
-            }
-
-            @Override
-            public void onStopDiscoveryFailed(String serviceType, int errorCode) {
-                Log.e(TAG, "Discovery failed: Error code: " + errorCode);
-                nsdManager.stopServiceDiscovery(this);
-                multicastReleaser.run();
-            }
-        };
-
-        nsdManager.discoverServices(
-                serviceType, NsdManager.PROTOCOL_DNS_SD, discoveryListener
-        );
-    }
-
-    private void connectToChild(final String address, final int port, final String name) {
-        final Intent i = new Intent(getApplicationContext(), ListenActivity.class);
-        final Bundle b = new Bundle();
-        b.putString("address", address);
-        b.putInt("port", port);
-        b.putString("name", name);
-        i.putExtras(b);
-        startActivity(i);
-    }
-}
-
-class ServiceInfoWrapper {
-    private final NsdServiceInfo info;
-    public ServiceInfoWrapper(NsdServiceInfo info)
-    {
-        this.info = info;
-    }
-
-    public boolean matches(NsdServiceInfo other) {
-        return Objects.equals(this.info.getHost(), other.getHost()) && this.info.getPort() == other.getPort();
-    }
-
-    public String getAddress()
-    {
-        return info.getHost().getHostAddress();
-    }
-
-    public int getPort()
-    {
-        return info.getPort();
-    }
-
-    public String getName() {
-        // If there is more than one service with the same name on the network, it will
-        // have a number at the end, but will appear as the following:
-        //   "ChildMonitor\\032(number)
-        // or
-        //   "ChildMonitor\032(number)
-        // Replace \\032 and \032 with a " "
-        String serviceName = info.getServiceName();
-        serviceName = serviceName.replace("\\\\032", " ");
-        serviceName = serviceName.replace("\\032", " ");
-        return serviceName;
-    }
-
-    @Override
-    public String toString()
-    {
-        return getName();
-    }
-}
diff --git a/app/src/main/java/de/rochefort/childmonitor/DiscoverActivity.kt b/app/src/main/java/de/rochefort/childmonitor/DiscoverActivity.kt
new file mode 100644
index 0000000..0cd56ad
--- /dev/null
+++ b/app/src/main/java/de/rochefort/childmonitor/DiscoverActivity.kt
@@ -0,0 +1,247 @@
+/*
+ * This file is part of Child Monitor.
+ *
+ * Child Monitor is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Child Monitor is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
+ */
+package de.rochefort.childmonitor
+
+import android.app.Activity
+import android.content.Intent
+import android.net.nsd.NsdManager
+import android.net.nsd.NsdManager.DiscoveryListener
+import android.net.nsd.NsdServiceInfo
+import android.net.wifi.WifiManager
+import android.os.Bundle
+import android.util.Log
+import android.view.View
+import android.widget.AdapterView
+import android.widget.AdapterView.OnItemClickListener
+import android.widget.ArrayAdapter
+import android.widget.Button
+import android.widget.EditText
+import android.widget.ListView
+import android.widget.Toast
+
+val TAG = "ChildMonitor"
+
+class DiscoverActivity : Activity() {
+    private var nsdManager: NsdManager? = null
+    private var discoveryListener: DiscoveryListener? = null
+    override fun onCreate(savedInstanceState: Bundle?) {
+        Log.i(TAG, "ChildMonitor start")
+        nsdManager = this.getSystemService(NSD_SERVICE) as NsdManager
+        super.onCreate(savedInstanceState)
+        setContentView(R.layout.activity_discover)
+        val discoverChildButton = findViewById<Button>(R.id.discoverChildButton)
+        discoverChildButton.setOnClickListener { v: View? -> loadDiscoveryViaMdns() }
+        val enterChildAddressButton = findViewById<Button>(R.id.enterChildAddressButton)
+        enterChildAddressButton.setOnClickListener { v: View? -> loadDiscoveryViaAddress() }
+    }
+
+    private fun loadDiscoveryViaMdns() {
+        setContentView(R.layout.activity_discover_mdns)
+        startServiceDiscovery("_childmonitor._tcp.")
+    }
+
+    private fun loadDiscoveryViaAddress() {
+        setContentView(R.layout.activity_discover_address)
+        val connectButton = findViewById<Button>(R.id.connectViaAddressButton)
+        val addressField = findViewById<EditText>(R.id.ipAddressField)
+        val portField = findViewById<EditText>(R.id.portField)
+        val preferredAddress = getPreferences(MODE_PRIVATE).getString(PREF_KEY_CHILD_DEVICE_ADDRESS, null)
+        if (!preferredAddress.isNullOrEmpty()) {
+            addressField.setText(preferredAddress)
+        }
+        val preferredPort = getPreferences(MODE_PRIVATE).getInt(PREF_KEY_CHILD_DEVICE_PORT, -1)
+        if (preferredPort > 0) {
+            portField.setText(preferredPort.toString())
+        } else {
+            portField.setText("10000")
+        }
+        connectButton.setOnClickListener { v: View? ->
+            Log.i(TAG, "Connecting to child device via address")
+            val addressString = addressField.text.toString()
+            val portString = portField.text.toString()
+            if (addressString.isEmpty()) {
+                Toast.makeText(this@DiscoverActivity, R.string.invalidAddress, Toast.LENGTH_LONG).show()
+                return@setOnClickListener
+            }
+            val port: Int = try {
+                portString.toInt()
+            } catch (e: NumberFormatException) {
+                Toast.makeText(this@DiscoverActivity, R.string.invalidPort, Toast.LENGTH_LONG).show()
+                return@setOnClickListener
+            }
+            val preferencesEditor = getPreferences(MODE_PRIVATE).edit()
+            preferencesEditor.putString(PREF_KEY_CHILD_DEVICE_ADDRESS, addressString)
+            preferencesEditor.putInt(PREF_KEY_CHILD_DEVICE_PORT, port)
+            preferencesEditor.apply()
+            connectToChild(addressString, port, addressString)
+        }
+    }
+
+    override fun onDestroy() {
+        Log.i(TAG, "ChildMonitoring stop")
+        if (discoveryListener != null) {
+            Log.i(TAG, "Unregistering monitoring service")
+            nsdManager!!.stopServiceDiscovery(discoveryListener)
+            discoveryListener = null
+        }
+        super.onDestroy()
+    }
+
+    fun startServiceDiscovery(serviceType: String) {
+        val nsdManager = this.getSystemService(NSD_SERVICE) as NsdManager
+        if (nsdManager == null) {
+            Log.e(TAG, "Could not obtain nsdManager")
+            return
+        }
+        val wifi = this.applicationContext.getSystemService(WIFI_SERVICE) as WifiManager
+        val multicastReleaser: Runnable
+        multicastReleaser = if (wifi != null) {
+            val multicastLock = wifi.createMulticastLock("multicastLock")
+            multicastLock.setReferenceCounted(true)
+            multicastLock.acquire()
+            Runnable {
+                try {
+                    multicastLock.release()
+                } catch (ignored: Exception) {
+                    //dont really care
+                }
+            }
+        } else {
+            Runnable {}
+        }
+        val serviceTable = findViewById<ListView>(R.id.ServiceTable)
+        val availableServicesAdapter = ArrayAdapter<ServiceInfoWrapper>(this,
+                R.layout.available_children_list)
+        serviceTable.adapter = availableServicesAdapter
+        serviceTable.onItemClickListener = OnItemClickListener { parent: AdapterView<*>, view: View?, position: Int, id: Long ->
+            val info = parent.getItemAtPosition(position) as ServiceInfoWrapper
+            connectToChild(info.address, info.port, info.name)
+        }
+
+        // Instantiate a new DiscoveryListener
+        discoveryListener = object : DiscoveryListener {
+            //  Called as soon as service discovery begins.
+            override fun onDiscoveryStarted(regType: String) {
+                Log.d(TAG, "Service discovery started")
+            }
+
+            override fun onServiceFound(service: NsdServiceInfo) {
+                // A service was found!  Do something with it.
+                Log.d(TAG, "Service discovery success: $service")
+                if (service.serviceType != serviceType) {
+                    // Service type is the string containing the protocol and
+                    // transport layer for this service.
+                    Log.d(TAG, "Unknown Service Type: " + service.serviceType)
+                } else if (service.serviceName.contains("ChildMonitor")) {
+                    val resolver: NsdManager.ResolveListener = object : NsdManager.ResolveListener {
+                        override fun onResolveFailed(serviceInfo: NsdServiceInfo, errorCode: Int) {
+                            // Called when the resolve fails.  Use the error code to debug.
+                            Log.e(TAG, "Resolve failed: error $errorCode for service: $serviceInfo")
+                        }
+
+                        override fun onServiceResolved(serviceInfo: NsdServiceInfo) {
+                            Log.i(TAG, "Resolve Succeeded: $serviceInfo")
+                            runOnUiThread {
+                                for (index in 0 until availableServicesAdapter.count) {
+                                    val item = availableServicesAdapter.getItem(index)
+                                    if (item != null && item.matches(serviceInfo)) {
+                                        // Prevent inserting duplicates
+                                        return@runOnUiThread
+                                    }
+                                }
+                                availableServicesAdapter.add(ServiceInfoWrapper(serviceInfo))
+                            }
+                        }
+                    }
+                    this@DiscoverActivity.nsdManager!!.resolveService(service, resolver)
+                } else {
+                    Log.d(TAG, "Unknown Service name: " + service.serviceName)
+                }
+            }
+
+            override fun onServiceLost(service: NsdServiceInfo) {
+                // When the network service is no longer available.
+                // Internal bookkeeping code goes here.
+                Log.e(TAG, "Service lost: $service")
+                multicastReleaser.run()
+            }
+
+            override fun onDiscoveryStopped(serviceType: String) {
+                Log.i(TAG, "Discovery stopped: $serviceType")
+                multicastReleaser.run()
+            }
+
+            override fun onStartDiscoveryFailed(serviceType: String, errorCode: Int) {
+                Log.e(TAG, "Discovery failed: Error code: $errorCode")
+                nsdManager.stopServiceDiscovery(this)
+                multicastReleaser.run()
+            }
+
+            override fun onStopDiscoveryFailed(serviceType: String, errorCode: Int) {
+                Log.e(TAG, "Discovery failed: Error code: $errorCode")
+                nsdManager.stopServiceDiscovery(this)
+                multicastReleaser.run()
+            }
+        }
+        nsdManager.discoverServices(
+                serviceType, NsdManager.PROTOCOL_DNS_SD, discoveryListener
+        )
+    }
+
+    private fun connectToChild(address: String, port: Int, name: String) {
+        val i = Intent(applicationContext, ListenActivity::class.java)
+        val b = Bundle()
+        b.putString("address", address)
+        b.putInt("port", port)
+        b.putString("name", name)
+        i.putExtras(b)
+        startActivity(i)
+    }
+
+    companion object {
+        private const val PREF_KEY_CHILD_DEVICE_ADDRESS = "childDeviceAddress"
+        private const val PREF_KEY_CHILD_DEVICE_PORT = "childDevicePort"
+    }
+}
+
+internal class ServiceInfoWrapper(private val info: NsdServiceInfo) {
+    fun matches(other: NsdServiceInfo): Boolean {
+        return info.host == other.host && info.port == other.port
+    }
+
+    val address: String
+        get() = info.host.hostAddress
+    val port: Int
+        get() = info.port
+    val name: String
+        get() {
+            // If there is more than one service with the same name on the network, it will
+            // have a number at the end, but will appear as the following:
+            //   "ChildMonitor\\032(number)
+            // or
+            //   "ChildMonitor\032(number)
+            // Replace \\032 and \032 with a " "
+            var serviceName = info.serviceName
+            serviceName = serviceName.replace("\\\\032", " ")
+            serviceName = serviceName.replace("\\032", " ")
+            return serviceName
+        }
+
+    override fun toString(): String {
+        return name
+    }
+}
diff --git a/app/src/main/java/de/rochefort/childmonitor/ListenActivity.java b/app/src/main/java/de/rochefort/childmonitor/ListenActivity.java
deleted file mode 100644
index 557e823..0000000
--- a/app/src/main/java/de/rochefort/childmonitor/ListenActivity.java
+++ /dev/null
@@ -1,127 +0,0 @@
-/*
- * This file is part of Child Monitor.
- *
- * Child Monitor is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Child Monitor is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
- */
-package de.rochefort.childmonitor;
-
-import android.app.Activity;
-import android.content.ComponentName;
-import android.content.Context;
-import android.content.Intent;
-import android.content.ServiceConnection;
-import android.media.AudioManager;
-import android.os.Bundle;
-import android.os.IBinder;
-import android.support.v4.content.ContextCompat;
-import android.util.Log;
-import android.widget.TextView;
-import android.widget.Toast;
-
-public class ListenActivity extends Activity {
-    private static final String TAG = "ListenActivity";
-
-    // Don't attempt to unbind from the service unless the client has received some
-    // information about the service's state.
-    private boolean shouldUnbind;
-
-    private final ServiceConnection connection = new ServiceConnection() {
-        public void onServiceConnected(ComponentName className, IBinder service) {
-            // This is called when the connection with the service has been
-            // established, giving us the service object we can use to
-            // interact with the service.  Because we have bound to a explicit
-            // service that we know is running in our own process, we can
-            // cast its IBinder to a concrete class and directly access it.
-            ListenService bs = ((ListenService.ListenBinder) service).getService();
-
-            Toast.makeText(ListenActivity.this, R.string.connect,
-                    Toast.LENGTH_SHORT).show();
-            final TextView connectedText = findViewById(R.id.connectedTo);
-            connectedText.setText(bs.getChildDeviceName());
-            final VolumeView volumeView = findViewById(R.id.volume);
-            volumeView.setVolumeHistory(bs.getVolumeHistory());
-            bs.setUpdateCallback(volumeView::postInvalidate);
-            bs.setErrorCallback(ListenActivity.this::postErrorMessage);
-        }
-
-        public void onServiceDisconnected(ComponentName className) {
-            // This is called when the connection with the service has been
-            // unexpectedly disconnected -- that is, its process crashed.
-            // Because it is running in our same process, we should never
-            // see this happen.
-            Toast.makeText(ListenActivity.this, R.string.disconnected,
-                    Toast.LENGTH_SHORT).show();
-        }
-    };
-
-
-    void ensureServiceRunningAndBind(Bundle bundle) {
-        final Context context = this;
-        final Intent intent = new Intent(context, ListenService.class);
-        if (bundle != null) {
-            intent.putExtra("name", bundle.getString("name"));
-            intent.putExtra("address", bundle.getString("address"));
-            intent.putExtra("port", bundle.getInt("port"));
-            ContextCompat.startForegroundService(context, intent);
-        }
-        // Attempts to establish a connection with the service.  We use an
-        // explicit class name because we want a specific service
-        // implementation that we know will be running in our own process
-        // (and thus won't be supporting component replacement by other
-        // applications).
-        if (bindService(intent, connection, Context.BIND_AUTO_CREATE)) {
-            shouldUnbind = true;
-            Log.i(TAG, "Bound listen service");
-        } else {
-            Log.e(TAG, "Error: The requested service doesn't " +
-                    "exist, or this client isn't allowed access to it.");
-        }
-    }
-
-    void doUnbindAndStopService() {
-        if (shouldUnbind) {
-            // Release information about the service's state.
-            unbindService(connection);
-            shouldUnbind = false;
-        }
-        final Context context = this;
-        final Intent intent = new Intent(context, ListenService.class);
-        context.stopService(intent);
-    }
-
-    public void postErrorMessage() {
-        TextView status = findViewById(R.id.textStatus);
-        status.post(() -> status.setText(R.string.disconnected));
-    }
-
-    @Override
-    protected void onCreate(Bundle savedInstanceState) {
-        super.onCreate(savedInstanceState);
-
-        final Bundle bundle = getIntent().getExtras();
-        ensureServiceRunningAndBind(bundle);
-
-        setVolumeControlStream(AudioManager.STREAM_MUSIC);
-        setContentView(R.layout.activity_listen);
-
-        final TextView statusText = findViewById(R.id.textStatus);
-        statusText.setText(R.string.listening);
-    }
-
-    @Override
-    public void onDestroy() {
-        doUnbindAndStopService();
-        super.onDestroy();
-    }
-}
diff --git a/app/src/main/java/de/rochefort/childmonitor/ListenActivity.kt b/app/src/main/java/de/rochefort/childmonitor/ListenActivity.kt
new file mode 100644
index 0000000..43b7051
--- /dev/null
+++ b/app/src/main/java/de/rochefort/childmonitor/ListenActivity.kt
@@ -0,0 +1,122 @@
+/*
+ * This file is part of Child Monitor.
+ *
+ * Child Monitor is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Child Monitor is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
+ */
+package de.rochefort.childmonitor
+
+import android.app.Activity
+import android.content.ComponentName
+import android.content.Context
+import android.content.Intent
+import android.content.ServiceConnection
+import android.media.AudioManager
+import android.os.Bundle
+import android.os.IBinder
+import android.util.Log
+import android.widget.TextView
+import android.widget.Toast
+import androidx.core.content.ContextCompat
+import de.rochefort.childmonitor.ListenService.ListenBinder
+
+class ListenActivity : Activity() {
+    // Don't attempt to unbind from the service unless the client has received some
+    // information about the service's state.
+    private var shouldUnbind = false
+    private val connection: ServiceConnection = object : ServiceConnection {
+        override fun onServiceConnected(className: ComponentName, service: IBinder) {
+            // This is called when the connection with the service has been
+            // established, giving us the service object we can use to
+            // interact with the service.  Because we have bound to a explicit
+            // service that we know is running in our own process, we can
+            // cast its IBinder to a concrete class and directly access it.
+            val bs = (service as ListenBinder).service
+            Toast.makeText(this@ListenActivity, R.string.connect,
+                    Toast.LENGTH_SHORT).show()
+            val connectedText = findViewById<TextView>(R.id.connectedTo)
+            connectedText.text = bs.childDeviceName
+            val volumeView = findViewById<VolumeView>(R.id.volume)
+            volumeView.setVolumeHistory(bs.volumeHistory)
+            bs.setUpdateCallback { volumeView.postInvalidate() }
+            bs.setErrorCallback { postErrorMessage() }
+        }
+
+        override fun onServiceDisconnected(className: ComponentName) {
+            // This is called when the connection with the service has been
+            // unexpectedly disconnected -- that is, its process crashed.
+            // Because it is running in our same process, we should never
+            // see this happen.
+            Toast.makeText(this@ListenActivity, R.string.disconnected,
+                    Toast.LENGTH_SHORT).show()
+        }
+    }
+
+    private fun ensureServiceRunningAndBind(bundle: Bundle?) {
+        val context: Context = this
+        val intent = Intent(context, ListenService::class.java)
+        if (bundle != null) {
+            intent.putExtra("name", bundle.getString("name"))
+            intent.putExtra("address", bundle.getString("address"))
+            intent.putExtra("port", bundle.getInt("port"))
+            ContextCompat.startForegroundService(context, intent)
+        }
+        // Attempts to establish a connection with the service.  We use an
+        // explicit class name because we want a specific service
+        // implementation that we know will be running in our own process
+        // (and thus won't be supporting component replacement by other
+        // applications).
+        if (bindService(intent, connection, BIND_AUTO_CREATE)) {
+            this.shouldUnbind = true
+            Log.i(TAG, "Bound listen service")
+        } else {
+            Log.e(TAG, "Error: The requested service doesn't " +
+                    "exist, or this client isn't allowed access to it.")
+        }
+    }
+
+    private fun doUnbindAndStopService() {
+        if (this.shouldUnbind) {
+            // Release information about the service's state.
+            unbindService(connection)
+            this.shouldUnbind = false
+        }
+        val context: Context = this
+        val intent = Intent(context, ListenService::class.java)
+        context.stopService(intent)
+    }
+
+    fun postErrorMessage() {
+        val status = findViewById<TextView>(R.id.textStatus)
+        status.post { status.setText(R.string.disconnected) }
+    }
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        val bundle = this.intent.extras
+        ensureServiceRunningAndBind(bundle)
+        this.volumeControlStream = AudioManager.STREAM_MUSIC
+        setContentView(R.layout.activity_listen)
+        val statusText = findViewById<TextView>(R.id.textStatus)
+        statusText.setText(R.string.listening)
+    }
+
+    public override fun onDestroy() {
+        doUnbindAndStopService()
+        super.onDestroy()
+    }
+
+    companion object {
+        private const val TAG = "ListenActivity"
+    }
+}
diff --git a/app/src/main/java/de/rochefort/childmonitor/ListenService.java b/app/src/main/java/de/rochefort/childmonitor/ListenService.java
deleted file mode 100644
index badacec..0000000
--- a/app/src/main/java/de/rochefort/childmonitor/ListenService.java
+++ /dev/null
@@ -1,246 +0,0 @@
-/*
- * This file is part of Child Monitor.
- *
- * Child Monitor is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Child Monitor is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
- */
-package de.rochefort.childmonitor;
-
-import static de.rochefort.childmonitor.AudioCodecDefines.CODEC;
-
-import android.app.Notification;
-import android.app.NotificationChannel;
-import android.app.NotificationManager;
-import android.app.PendingIntent;
-import android.app.Service;
-import android.content.Intent;
-import android.media.AudioManager;
-import android.media.AudioTrack;
-import android.media.MediaPlayer;
-import android.os.Binder;
-import android.os.Build;
-import android.os.Bundle;
-import android.os.IBinder;
-import android.support.v4.app.NotificationCompat;
-import android.util.Log;
-import android.widget.Toast;
-
-import java.io.IOException;
-import java.io.InputStream;
-import java.net.Socket;
-
-public class ListenService extends Service {
-    private static final String TAG = "ListenService";
-    public static final String CHANNEL_ID = TAG;
-    public static final int ID = 902938409;
-
-    private final int frequency = AudioCodecDefines.FREQUENCY;
-    private final int channelConfiguration = AudioCodecDefines.CHANNEL_CONFIGURATION_OUT;
-    private final int audioEncoding = AudioCodecDefines.ENCODING;
-    private final int bufferSize = AudioTrack.getMinBufferSize(frequency, channelConfiguration, audioEncoding);
-    private final int byteBufferSize = bufferSize*2;
-
-    private final IBinder binder = new ListenBinder();
-    private NotificationManager notificationManager;
-    private Thread listenThread;
-
-    private final VolumeHistory volumeHistory = new VolumeHistory(16_384);
-    private String childDeviceName;
-
-    public ListenService() {
-    }
-
-    @Override
-    public void onCreate() {
-        super.onCreate();
-        notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
-    }
-
-    @Override
-    public int onStartCommand(Intent intent, int flags, int startId) {
-        Log.i(TAG, "Received start id " + startId + ": " + intent);
-        // Display a notification about us starting.  We put an icon in the status bar.
-        createNotificationChannel();
-        Bundle extras = intent.getExtras();
-        if (extras != null) {
-            String name = extras.getString("name");
-            childDeviceName = name;
-            Notification n = buildNotification(name);
-            startForeground(ID, n);
-            String address = extras.getString("address");
-            int port = extras.getInt("port");
-            doListen(address, port);
-        }
-
-        return START_REDELIVER_INTENT;
-    }
-
-    @Override
-    public void onDestroy() {
-        Thread lt = listenThread;
-        if (lt != null) {
-            lt.interrupt();
-            listenThread = null;
-        }
-
-        // Cancel the persistent notification.
-        int NOTIFICATION = R.string.listening;
-        notificationManager.cancel(NOTIFICATION);
-
-        stopForeground(true);
-        // Tell the user we stopped.
-        Toast.makeText(this, R.string.stopped, Toast.LENGTH_SHORT).show();
-    }
-
-    @Override
-    public IBinder onBind(Intent intent) {
-        return binder;
-    }
-
-    public VolumeHistory getVolumeHistory() {
-        return volumeHistory;
-    }
-
-    private Notification buildNotification(String name) {
-        // In this sample, we'll use the same text for the ticker and the expanded notification
-        CharSequence text = getText(R.string.listening);
-
-        // The PendingIntent to launch our activity if the user selects this notification
-        PendingIntent contentIntent = PendingIntent.getActivity(this, 0,
-                new Intent(this, ListenActivity.class), PendingIntent.FLAG_IMMUTABLE);
-
-        // Set the info for the views that show in the notification panel.
-        NotificationCompat.Builder b = new NotificationCompat.Builder(this, CHANNEL_ID);
-        b.setSmallIcon(R.drawable.listening_notification)  // the status icon
-                .setOngoing(true)
-                .setTicker(text)  // the status text
-                .setContentTitle(text)  // the label of the entry
-                .setContentText(name)  // the contents of the entry
-                .setContentIntent(contentIntent);
-        return b.build();
-    }
-
-
-    private void createNotificationChannel() {
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
-            NotificationChannel serviceChannel = new NotificationChannel(
-                    CHANNEL_ID,
-                    "Foreground Service Channel",
-                    NotificationManager.IMPORTANCE_DEFAULT
-            );
-            notificationManager.createNotificationChannel(serviceChannel);
-        }
-    }
-
-    public void setErrorCallback(Runnable errorCallback) {
-        this.mErrorCallback = errorCallback;
-    }
-
-    public void setUpdateCallback(Runnable updateCallback) {
-        this.mUpdateCallback = updateCallback;
-    }
-
-    public class ListenBinder extends Binder {
-        ListenService getService() {
-            return ListenService.this;
-        }
-    }
-
-    private Runnable mErrorCallback;
-    private Runnable mUpdateCallback;
-
-    private void doListen(String address, int port) {
-        Thread lt = new Thread(() -> {
-            try {
-                final Socket socket = new Socket(address, port);
-                streamAudio(socket);
-            } catch (IOException e) {
-                Log.e(TAG, "Failed to stream audio", e);
-            }
-
-            if (!Thread.currentThread().isInterrupted()) {
-                // If this thread has not been interrupted, likely something
-                // bad happened with the connection to the child device. Play
-                // an alert to notify the user that the connection has been
-                // interrupted.
-                playAlert();
-
-                final Runnable errorCallback = mErrorCallback;
-                if (errorCallback != null) {
-                    errorCallback.run();
-                }
-            }
-        });
-        listenThread = lt;
-        lt.start();
-    }
-
-
-    private void streamAudio(final Socket socket) throws IllegalArgumentException, IllegalStateException, IOException {
-        Log.i(TAG, "Setting up stream");
-
-        final AudioTrack audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,
-                frequency,
-                channelConfiguration,
-                audioEncoding,
-                bufferSize,
-                AudioTrack.MODE_STREAM);
-
-        final InputStream is = socket.getInputStream();
-        int read = 0;
-
-        audioTrack.play();
-
-        try {
-            final byte [] readBuffer = new byte[byteBufferSize];
-            final short [] decodedBuffer = new short[byteBufferSize*2];
-
-            while (socket.isConnected() && read != -1 && !Thread.currentThread().isInterrupted()) {
-                read = is.read(readBuffer);
-                int decoded = CODEC.decode(decodedBuffer, readBuffer, read, 0);
-
-                if (decoded > 0) {
-                    audioTrack.write(decodedBuffer, 0, decoded);
-                    short[] decodedBytes = new short[decoded];
-                    System.arraycopy(decodedBuffer, 0, decodedBytes, 0, decoded);
-                    volumeHistory.onAudioData(decodedBytes);
-                    final Runnable updateCallback = mUpdateCallback;
-                    if (updateCallback != null) {
-                        updateCallback.run();
-                    }
-                }
-            }
-        } catch (Exception e) {
-            Log.e(TAG, "Connection failed", e);
-        } finally {
-            audioTrack.stop();
-            socket.close();
-        }
-    }
-
-
-    private void playAlert() {
-        final MediaPlayer mp = MediaPlayer.create(this, R.raw.upward_beep_chromatic_fifths);
-        if(mp != null) {
-            Log.i(TAG, "Playing alert");
-            mp.setOnCompletionListener(MediaPlayer::release);
-            mp.start();
-        } else {
-            Log.e(TAG, "Failed to play alert");
-        }
-    }
-
-    public String getChildDeviceName() {
-        return childDeviceName;
-    }
-}
diff --git a/app/src/main/java/de/rochefort/childmonitor/ListenService.kt b/app/src/main/java/de/rochefort/childmonitor/ListenService.kt
new file mode 100644
index 0000000..7784f55
--- /dev/null
+++ b/app/src/main/java/de/rochefort/childmonitor/ListenService.kt
@@ -0,0 +1,212 @@
+/*
+ * This file is part of Child Monitor.
+ *
+ * Child Monitor is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Child Monitor is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
+ */
+package de.rochefort.childmonitor
+
+import android.app.Notification
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.app.PendingIntent
+import android.app.Service
+import android.content.Intent
+import android.content.pm.ServiceInfo
+import android.media.AudioManager
+import android.media.AudioTrack
+import android.media.MediaPlayer
+import android.os.Binder
+import android.os.Build
+import android.os.IBinder
+import android.util.Log
+import android.widget.Toast
+import androidx.core.app.NotificationCompat
+import androidx.core.app.ServiceCompat
+import java.io.IOException
+import java.net.Socket
+
+class ListenService : Service() {
+    private val frequency: Int = AudioCodecDefines.Companion.FREQUENCY
+    private val channelConfiguration: Int = AudioCodecDefines.Companion.CHANNEL_CONFIGURATION_OUT
+    private val audioEncoding: Int = AudioCodecDefines.Companion.ENCODING
+    private val bufferSize = AudioTrack.getMinBufferSize(frequency, channelConfiguration, audioEncoding)
+    private val byteBufferSize = bufferSize * 2
+    private val binder: IBinder = ListenBinder()
+    private var notificationManager: NotificationManager? = null
+    private var listenThread: Thread? = null
+    val volumeHistory = VolumeHistory(16384)
+    var childDeviceName: String? = null
+        private set
+
+    override fun onCreate() {
+        super.onCreate()
+        this.notificationManager = getSystemService(NOTIFICATION_SERVICE) as NotificationManager
+    }
+
+    override fun onStartCommand(intent: Intent, flags: Int, startId: Int): Int {
+        Log.i(TAG, "Received start id $startId: $intent")
+        // Display a notification about us starting.  We put an icon in the status bar.
+        createNotificationChannel()
+        val extras = intent.extras
+        if (extras != null) {
+            val name = extras.getString("name")
+            childDeviceName = name
+            val n = buildNotification(name)
+            val foregroundServiceType = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) ServiceInfo.FOREGROUND_SERVICE_TYPE_MEDIA_PLAYBACK else 0 // Keep the linter happy
+            ServiceCompat.startForeground(this, ID, n, foregroundServiceType)
+            val address = extras.getString("address")
+            val port = extras.getInt("port")
+            doListen(address, port)
+        }
+        return START_REDELIVER_INTENT
+    }
+
+    override fun onDestroy() {
+        val lt = this.listenThread
+        if (lt != null) {
+            lt.interrupt()
+            this.listenThread = null
+        }
+
+        // Cancel the persistent notification.
+        val NOTIFICATION = R.string.listening
+        notificationManager!!.cancel(NOTIFICATION)
+        ServiceCompat.stopForeground(this, ServiceCompat.STOP_FOREGROUND_REMOVE)
+        // Tell the user we stopped.
+        Toast.makeText(this, R.string.stopped, Toast.LENGTH_SHORT).show()
+    }
+
+    override fun onBind(intent: Intent): IBinder {
+        return binder
+    }
+
+    private fun buildNotification(name: String?): Notification {
+        // In this sample, we'll use the same text for the ticker and the expanded notification
+        val text = getText(R.string.listening)
+
+        // The PendingIntent to launch our activity if the user selects this notification
+        val contentIntent = PendingIntent.getActivity(this, 0,
+                Intent(this, ListenActivity::class.java), PendingIntent.FLAG_IMMUTABLE)
+
+        // Set the info for the views that show in the notification panel.
+        val b = NotificationCompat.Builder(this, CHANNEL_ID)
+        b.setSmallIcon(R.drawable.listening_notification) // the status icon
+                .setOngoing(true)
+                .setTicker(text) // the status text
+                .setContentTitle(text) // the label of the entry
+                .setContentText(name) // the contents of the entry
+                .setContentIntent(contentIntent)
+        return b.build()
+    }
+
+    private fun createNotificationChannel() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            val serviceChannel = NotificationChannel(
+                    CHANNEL_ID,
+                    "Foreground Service Channel",
+                    NotificationManager.IMPORTANCE_DEFAULT
+            )
+            notificationManager!!.createNotificationChannel(serviceChannel)
+        }
+    }
+
+    fun setErrorCallback(errorCallback: Runnable?) {
+        mErrorCallback = errorCallback
+    }
+
+    fun setUpdateCallback(updateCallback: Runnable?) {
+        mUpdateCallback = updateCallback
+    }
+
+    inner class ListenBinder : Binder() {
+        val service: ListenService
+            get() = this@ListenService
+    }
+
+    private var mErrorCallback: Runnable? = null
+    private var mUpdateCallback: Runnable? = null
+    private fun doListen(address: String?, port: Int) {
+        val lt = Thread {
+            try {
+                val socket = Socket(address, port)
+                streamAudio(socket)
+            } catch (e: IOException) {
+                Log.e(TAG, "Failed to stream audio", e)
+            }
+            if (!Thread.currentThread().isInterrupted) {
+                // If this thread has not been interrupted, likely something
+                // bad happened with the connection to the child device. Play
+                // an alert to notify the user that the connection has been
+                // interrupted.
+                playAlert()
+                val errorCallback = mErrorCallback
+                errorCallback?.run()
+            }
+        }
+        this.listenThread = lt
+        lt.start()
+    }
+
+    @Throws(IllegalArgumentException::class, IllegalStateException::class, IOException::class)
+    private fun streamAudio(socket: Socket) {
+        Log.i(TAG, "Setting up stream")
+        val audioTrack = AudioTrack(AudioManager.STREAM_MUSIC,
+                frequency,
+                channelConfiguration,
+                audioEncoding,
+                bufferSize,
+                AudioTrack.MODE_STREAM)
+        val inputStream = socket.getInputStream()
+        var read = 0
+        audioTrack.play()
+        try {
+            val readBuffer = ByteArray(byteBufferSize)
+            val decodedBuffer = ShortArray(byteBufferSize * 2)
+            while (socket.isConnected && read != -1 && !Thread.currentThread().isInterrupted) {
+                read = inputStream.read(readBuffer)
+                val decoded: Int = AudioCodecDefines.Companion.CODEC.decode(decodedBuffer, readBuffer, read, 0)
+                if (decoded > 0) {
+                    audioTrack.write(decodedBuffer, 0, decoded)
+                    val decodedBytes = ShortArray(decoded)
+                    System.arraycopy(decodedBuffer, 0, decodedBytes, 0, decoded)
+                    volumeHistory.onAudioData(decodedBytes)
+                    val updateCallback = mUpdateCallback
+                    updateCallback?.run()
+                }
+            }
+        } catch (e: Exception) {
+            Log.e(TAG, "Connection failed", e)
+        } finally {
+            audioTrack.stop()
+            socket.close()
+        }
+    }
+
+    private fun playAlert() {
+        val mp = MediaPlayer.create(this, R.raw.upward_beep_chromatic_fifths)
+        if (mp != null) {
+            Log.i(TAG, "Playing alert")
+            mp.setOnCompletionListener { obj: MediaPlayer -> obj.release() }
+            mp.start()
+        } else {
+            Log.e(TAG, "Failed to play alert")
+        }
+    }
+
+    companion object {
+        private const val TAG = "ListenService"
+        const val CHANNEL_ID = TAG
+        const val ID = 902938409
+    }
+}
diff --git a/app/src/main/java/de/rochefort/childmonitor/MonitorActivity.java b/app/src/main/java/de/rochefort/childmonitor/MonitorActivity.java
deleted file mode 100644
index 625697a..0000000
--- a/app/src/main/java/de/rochefort/childmonitor/MonitorActivity.java
+++ /dev/null
@@ -1,143 +0,0 @@
-/*
- * This file is part of Child Monitor.
- *
- * Child Monitor is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Child Monitor is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
- */
-package de.rochefort.childmonitor;
-
-import android.app.Activity;
-import android.content.ComponentName;
-import android.content.Context;
-import android.content.Intent;
-import android.content.ServiceConnection;
-import android.net.ConnectivityManager;
-import android.net.LinkAddress;
-import android.net.Network;
-import android.net.NetworkInfo;
-import android.os.Bundle;
-import android.os.IBinder;
-import android.support.v4.content.ContextCompat;
-import android.util.Log;
-import android.widget.TextView;
-import android.widget.Toast;
-
-import java.net.InetAddress;
-import java.util.ArrayList;
-import java.util.List;
-
-public class MonitorActivity extends Activity {
-    final static String TAG = "ChildMonitor";
-    private final ServiceConnection connection = new ServiceConnection() {
-        public void onServiceConnected(ComponentName className, IBinder service) {
-            // This is called when the connection with the service has been
-            // established, giving us the service object we can use to
-            // interact with the service. Because we have bound to an explicit
-            // service that we know is running in our own process, we can
-            // cast its IBinder to a concrete class and directly access it.
-            MonitorService bs = ((MonitorService.MonitorBinder) service).getService();
-            bs.setMonitorActivity(MonitorActivity.this);
-        }
-
-        public void onServiceDisconnected(ComponentName className) {
-            // This is called when the connection with the service has been
-            // unexpectedly disconnected -- that is, its process crashed.
-            // Because it is running in our same process, we should never
-            // see this happen.
-            Toast.makeText(MonitorActivity.this, R.string.disconnected,
-                    Toast.LENGTH_SHORT).show();
-        }
-    };
-    private boolean shouldUnbind;
-
-    @Override
-    protected void onCreate(Bundle savedInstanceState) {
-        Log.i(TAG, "ChildMonitor start");
-        super.onCreate(savedInstanceState);
-        setContentView(R.layout.activity_monitor);
-        final TextView addressText = findViewById(R.id.address);
-
-        List<String> listenAddresses = getListenAddresses();
-        if (!listenAddresses.isEmpty()) {
-            StringBuilder sb = new StringBuilder();
-            for (int i = 0; i < listenAddresses.size(); i++) {
-                String listenAddress = listenAddresses.get(i);
-                sb.append(listenAddress);
-                if (i != listenAddresses.size() - 1) {
-                    sb.append("\n\n");
-                }
-            }
-            addressText.setText(sb.toString());
-        } else {
-            addressText.setText(R.string.notConnected);
-        }
-
-        ensureServiceRunningAndBind();
-    }
-
-    private List<String> getListenAddresses() {
-        ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
-        List<String> listenAddresses = new ArrayList<>();
-        if (cm != null) {
-            for (Network network : cm.getAllNetworks()) {
-                NetworkInfo networkInfo = cm.getNetworkInfo(network);
-                boolean connected = networkInfo.isConnected();
-                if (connected) {
-                    List<LinkAddress> linkAddresses = cm.getLinkProperties(network).getLinkAddresses();
-                    for (LinkAddress linkAddress : linkAddresses) {
-                        InetAddress address = linkAddress.getAddress();
-                        if (!address.isLinkLocalAddress() && !address.isLoopbackAddress()) {
-                            listenAddresses.add(address.getHostAddress() + " (" + networkInfo.getTypeName() + ")");
-                        }
-                    }
-                }
-            }
-        }
-        return listenAddresses;
-    }
-
-    @Override
-    public void onDestroy() {
-        doUnbindAndStopService();
-        super.onDestroy();
-    }
-
-    void ensureServiceRunningAndBind() {
-        final Context context = this;
-        final Intent intent = new Intent(context, MonitorService.class);
-        ContextCompat.startForegroundService(context, intent);
-        // Attempts to establish a connection with the service.  We use an
-        // explicit class name because we want a specific service
-        // implementation that we know will be running in our own process
-        // (and thus won't be supporting component replacement by other
-        // applications).
-        if (bindService(intent, connection, Context.BIND_AUTO_CREATE)) {
-            shouldUnbind = true;
-            Log.i(TAG, "Bound monitor service");
-        } else {
-            Log.e(TAG, "Error: The requested service doesn't " +
-                    "exist, or this client isn't allowed access to it.");
-        }
-    }
-
-    void doUnbindAndStopService() {
-        if (shouldUnbind) {
-            // Release information about the service's state.
-            unbindService(connection);
-            shouldUnbind = false;
-        }
-        final Context context = this;
-        final Intent intent = new Intent(context, MonitorService.class);
-        context.stopService(intent);
-    }
-}
diff --git a/app/src/main/java/de/rochefort/childmonitor/MonitorActivity.kt b/app/src/main/java/de/rochefort/childmonitor/MonitorActivity.kt
new file mode 100644
index 0000000..30a2565
--- /dev/null
+++ b/app/src/main/java/de/rochefort/childmonitor/MonitorActivity.kt
@@ -0,0 +1,134 @@
+/*
+ * This file is part of Child Monitor.
+ *
+ * Child Monitor is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Child Monitor is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
+ */
+package de.rochefort.childmonitor
+
+import android.app.Activity
+import android.content.ComponentName
+import android.content.Context
+import android.content.Intent
+import android.content.ServiceConnection
+import android.net.ConnectivityManager
+import android.os.Bundle
+import android.os.IBinder
+import android.util.Log
+import android.widget.TextView
+import android.widget.Toast
+import androidx.core.content.ContextCompat
+import de.rochefort.childmonitor.MonitorService.MonitorBinder
+
+class MonitorActivity : Activity() {
+    private val connection: ServiceConnection = object : ServiceConnection {
+        override fun onServiceConnected(className: ComponentName, service: IBinder) {
+            // This is called when the connection with the service has been
+            // established, giving us the service object we can use to
+            // interact with the service. Because we have bound to an explicit
+            // service that we know is running in our own process, we can
+            // cast its IBinder to a concrete class and directly access it.
+            val bs = (service as MonitorBinder).service
+            bs!!.setMonitorActivity(this@MonitorActivity)
+        }
+
+        override fun onServiceDisconnected(className: ComponentName) {
+            // This is called when the connection with the service has been
+            // unexpectedly disconnected -- that is, its process crashed.
+            // Because it is running in our same process, we should never
+            // see this happen.
+            Toast.makeText(this@MonitorActivity, R.string.disconnected,
+                    Toast.LENGTH_SHORT).show()
+        }
+    }
+    private var shouldUnbind = false
+    override fun onCreate(savedInstanceState: Bundle?) {
+        Log.i(TAG, "ChildMonitor start")
+        super.onCreate(savedInstanceState)
+        setContentView(R.layout.activity_monitor)
+        val addressText = findViewById<TextView>(R.id.address)
+        val listenAddresses = listenAddresses
+        if (listenAddresses.isNotEmpty()) {
+            val sb = StringBuilder()
+            for (i in listenAddresses.indices) {
+                val listenAddress = listenAddresses[i]
+                sb.append(listenAddress)
+                if (i != listenAddresses.size - 1) {
+                    sb.append("\n\n")
+                }
+            }
+            addressText.text = sb.toString()
+        } else {
+            addressText.setText(R.string.notConnected)
+        }
+        ensureServiceRunningAndBind()
+    }
+
+    private val listenAddresses: List<String>
+        get() {
+            val cm = getSystemService(CONNECTIVITY_SERVICE) as ConnectivityManager
+            val listenAddresses: MutableList<String> = ArrayList()
+            for (network in cm.allNetworks) {
+                val networkInfo = cm.getNetworkInfo(network)
+                val connected = networkInfo!!.isConnected
+                if (connected) {
+                    val linkAddresses = cm.getLinkProperties(network)!!.linkAddresses
+                    for (linkAddress in linkAddresses) {
+                        val address = linkAddress.address
+                        if (!address.isLinkLocalAddress && !address.isLoopbackAddress) {
+                            listenAddresses.add(address.hostAddress + " (" + networkInfo.typeName + ")")
+                        }
+                    }
+                }
+            }
+            return listenAddresses
+        }
+
+    public override fun onDestroy() {
+        doUnbindAndStopService()
+        super.onDestroy()
+    }
+
+    private fun ensureServiceRunningAndBind() {
+        val context: Context = this
+        val intent = Intent(context, MonitorService::class.java)
+        ContextCompat.startForegroundService(context, intent)
+        // Attempts to establish a connection with the service.  We use an
+        // explicit class name because we want a specific service
+        // implementation that we know will be running in our own process
+        // (and thus won't be supporting component replacement by other
+        // applications).
+        if (bindService(intent, connection, BIND_AUTO_CREATE)) {
+            this.shouldUnbind = true
+            Log.i(TAG, "Bound monitor service")
+        } else {
+            Log.e(TAG, "Error: The requested service doesn't " +
+                    "exist, or this client isn't allowed access to it.")
+        }
+    }
+
+    private fun doUnbindAndStopService() {
+        if (this.shouldUnbind) {
+            // Release information about the service's state.
+            unbindService(connection)
+            this.shouldUnbind = false
+        }
+        val context: Context = this
+        val intent = Intent(context, MonitorService::class.java)
+        context.stopService(intent)
+    }
+
+    companion object {
+        const val TAG = "ChildMonitor"
+    }
+}
diff --git a/app/src/main/java/de/rochefort/childmonitor/MonitorService.java b/app/src/main/java/de/rochefort/childmonitor/MonitorService.java
deleted file mode 100644
index 9ac1642..0000000
--- a/app/src/main/java/de/rochefort/childmonitor/MonitorService.java
+++ /dev/null
@@ -1,313 +0,0 @@
-/*
- * This file is part of Child Monitor.
- *
- * Child Monitor is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Child Monitor is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
- */
-package de.rochefort.childmonitor;
-
-import static de.rochefort.childmonitor.AudioCodecDefines.CODEC;
-
-import android.app.Notification;
-import android.app.NotificationChannel;
-import android.app.NotificationManager;
-import android.app.Service;
-import android.content.Context;
-import android.content.Intent;
-import android.media.AudioRecord;
-import android.media.MediaRecorder;
-import android.net.nsd.NsdManager;
-import android.net.nsd.NsdServiceInfo;
-import android.os.Binder;
-import android.os.Build;
-import android.os.IBinder;
-import android.support.v4.app.NotificationCompat;
-import android.util.Log;
-import android.widget.TextView;
-import android.widget.Toast;
-
-import java.io.IOException;
-import java.io.OutputStream;
-import java.net.ServerSocket;
-import java.net.Socket;
-import java.util.Objects;
-
-public class MonitorService extends Service {
-    final static String TAG = "MonitorService";
-    final static String CHANNEL_ID = TAG;
-    public static final int ID = 1338;
-    private final IBinder binder = new MonitorBinder();
-    private NsdManager nsdManager;
-    private NsdManager.RegistrationListener registrationListener;
-    private ServerSocket currentSocket;
-    private Object connectionToken;
-    private int currentPort;
-    private NotificationManager notificationManager;
-    private Thread monitorThread;
-    private MonitorActivity monitorActivity;
-
-    public void setMonitorActivity(MonitorActivity monitorActivity) {
-        this.monitorActivity = monitorActivity;
-    }
-
-    private void serviceConnection(Socket socket) {
-        final MonitorActivity ma = monitorActivity;
-        if (ma != null) {
-            ma.runOnUiThread(() -> {
-                final TextView statusText = monitorActivity.findViewById(R.id.textStatus);
-                statusText.setText(R.string.streaming);
-            });
-        }
-
-        final int frequency = AudioCodecDefines.FREQUENCY;
-        final int channelConfiguration = AudioCodecDefines.CHANNEL_CONFIGURATION_IN;
-        final int audioEncoding = AudioCodecDefines.ENCODING;
-
-        final int bufferSize = AudioRecord.getMinBufferSize(frequency, channelConfiguration, audioEncoding);
-        final AudioRecord audioRecord;
-        try {
-            audioRecord = new AudioRecord(
-                    MediaRecorder.AudioSource.MIC,
-                    frequency,
-                    channelConfiguration,
-                    audioEncoding,
-                    bufferSize
-            );
-        } catch (SecurityException e) {
-            // This should never happen, we asked for permission before
-            throw new RuntimeException(e);
-        }
-
-        final int pcmBufferSize = bufferSize * 2;
-        final short[] pcmBuffer = new short[pcmBufferSize];
-        final byte[] ulawBuffer = new byte[pcmBufferSize];
-
-        try {
-            audioRecord.startRecording();
-            final OutputStream out = socket.getOutputStream();
-
-            socket.setSendBufferSize(pcmBufferSize);
-            Log.d(TAG, "Socket send buffer size: " + socket.getSendBufferSize());
-
-            while (socket.isConnected() && currentSocket != null && !Thread.currentThread().isInterrupted()) {
-                final int read = audioRecord.read(pcmBuffer, 0, bufferSize);
-                int encoded = CODEC.encode(pcmBuffer, read, ulawBuffer, 0);
-                out.write(ulawBuffer, 0, encoded);
-            }
-        } catch (Exception e) {
-            Log.e(TAG, "Connection failed", e);
-        } finally {
-            audioRecord.stop();
-        }
-    }
-
-
-    @Override
-    public void onCreate() {
-        Log.i(TAG, "ChildMonitor start");
-        super.onCreate();
-        notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
-
-        nsdManager = (NsdManager) this.getSystemService(Context.NSD_SERVICE);
-        currentPort = 10000;
-        currentSocket = null;
-    }
-
-    @Override
-    public int onStartCommand(Intent intent, int flags, int startId) {
-        Log.i(TAG, "Received start id " + startId + ": " + intent);
-        // Display a notification about us starting.  We put an icon in the status bar.
-        createNotificationChannel();
-        Notification n = buildNotification();
-        startForeground(ID, n);
-        ensureMonitorThread();
-
-        return START_REDELIVER_INTENT;
-    }
-
-    private void ensureMonitorThread() {
-        Thread mt = monitorThread;
-        if (mt != null && mt.isAlive()) {
-            return;
-        }
-
-        final Object currentToken = new Object();
-        connectionToken = currentToken;
-
-        mt = new Thread(() -> {
-            while (Objects.equals(connectionToken, currentToken)) {
-                try (ServerSocket serverSocket = new ServerSocket(currentPort)) {
-                    currentSocket = serverSocket;
-                    // Store the chosen port.
-                    final int localPort = serverSocket.getLocalPort();
-
-                    // Register the service so that parent devices can
-                    // locate the child device
-                    registerService(localPort);
-
-                    // Wait for a parent to find us and connect
-                    try (Socket socket = serverSocket.accept()) {
-                        Log.i(TAG, "Connection from parent device received");
-
-                        // We now have a client connection.
-                        // Unregister so no other clients will
-                        // attempt to connect
-                        unregisterService();
-                        serviceConnection(socket);
-                    }
-                } catch (Exception e) {
-                    if (Objects.equals(connectionToken, currentToken)) {
-                        // Just in case
-                        currentPort++;
-                        Log.e(TAG, "Failed to open server socket. Port increased to " + currentPort, e);
-                    }
-                }
-            }
-        });
-        monitorThread = mt;
-        mt.start();
-    }
-
-    private void registerService(final int port) {
-        final NsdServiceInfo serviceInfo = new NsdServiceInfo();
-        serviceInfo.setServiceName("ChildMonitor on " + Build.MODEL);
-        serviceInfo.setServiceType("_childmonitor._tcp.");
-        serviceInfo.setPort(port);
-
-        registrationListener = new NsdManager.RegistrationListener() {
-            @Override
-            public void onServiceRegistered(NsdServiceInfo nsdServiceInfo) {
-                // Save the service name.  Android may have changed it in order to
-                // resolve a conflict, so update the name you initially requested
-                // with the name Android actually used.
-                final String serviceName = nsdServiceInfo.getServiceName();
-
-                Log.i(TAG, "Service name: " + serviceName);
-
-                final MonitorActivity ma = monitorActivity;
-                if (ma != null) {
-                    ma.runOnUiThread(() -> {
-                        final TextView statusText = ma.findViewById(R.id.textStatus);
-                        statusText.setText(R.string.waitingForParent);
-
-                        final TextView serviceText = ma.findViewById(R.id.textService);
-                        serviceText.setText(serviceName);
-
-                        final TextView portText = ma.findViewById(R.id.port);
-                        portText.setText(Integer.toString(port));
-                    });
-                }
-
-            }
-
-            @Override
-            public void onRegistrationFailed(NsdServiceInfo serviceInfo, int errorCode) {
-                // Registration failed!  Put debugging code here to determine why.
-                Log.e(TAG, "Registration failed: " + errorCode);
-            }
-
-            @Override
-            public void onServiceUnregistered(NsdServiceInfo arg0) {
-                // Service has been unregistered.  This only happens when you call
-                // NsdManager.unregisterService() and pass in this listener.
-
-                Log.i(TAG, "Unregistering service");
-            }
-
-            @Override
-            public void onUnregistrationFailed(NsdServiceInfo serviceInfo, int errorCode) {
-                // Unregistration failed.  Put debugging code here to determine why.
-
-                Log.e(TAG, "Unregistration failed: " + errorCode);
-            }
-        };
-
-        nsdManager.registerService(
-                serviceInfo, NsdManager.PROTOCOL_DNS_SD, registrationListener);
-    }
-
-    private void unregisterService() {
-        NsdManager.RegistrationListener currentListener = registrationListener;
-        if (currentListener != null) {
-            Log.i(TAG, "Unregistering monitoring service");
-
-            nsdManager.unregisterService(currentListener);
-            registrationListener = null;
-        }
-    }
-
-    private void createNotificationChannel() {
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
-            NotificationChannel serviceChannel = new NotificationChannel(
-                    CHANNEL_ID,
-                    "Foreground Service Channel",
-                    NotificationManager.IMPORTANCE_DEFAULT
-            );
-            notificationManager.createNotificationChannel(serviceChannel);
-        }
-    }
-
-    private Notification buildNotification() {
-        CharSequence text = "Child Device";
-        // Set the info for the views that show in the notification panel.
-        NotificationCompat.Builder b = new NotificationCompat.Builder(this, CHANNEL_ID);
-        b.setSmallIcon(R.drawable.listening_notification)  // the status icon
-                .setOngoing(true)
-                .setTicker(text)  // the status text
-                .setContentTitle(text);  // the label of the entry
-        return b.build();
-    }
-
-
-    @Override
-    public void onDestroy() {
-        Thread mt = monitorThread;
-        if (mt != null) {
-            mt.interrupt();
-            monitorThread = null;
-        }
-
-        unregisterService();
-
-        connectionToken = null;
-        if (currentSocket != null) {
-            try {
-                currentSocket.close();
-                currentSocket = null;
-            } catch (IOException e) {
-                Log.e(TAG, "Failed to close active socket on port " + currentPort);
-            }
-        }
-
-        // Cancel the persistent notification.
-        int NOTIFICATION = R.string.listening;
-        notificationManager.cancel(NOTIFICATION);
-
-        stopForeground(true);
-        // Tell the user we stopped.
-        Toast.makeText(this, R.string.stopped, Toast.LENGTH_SHORT).show();
-        super.onDestroy();
-    }
-
-    @Override
-    public IBinder onBind(Intent intent) {
-        return binder;
-    }
-
-    public class MonitorBinder extends Binder {
-        MonitorService getService() {
-            return MonitorService.this;
-        }
-    }
-
-}
diff --git a/app/src/main/java/de/rochefort/childmonitor/MonitorService.kt b/app/src/main/java/de/rochefort/childmonitor/MonitorService.kt
new file mode 100644
index 0000000..b82798f
--- /dev/null
+++ b/app/src/main/java/de/rochefort/childmonitor/MonitorService.kt
@@ -0,0 +1,273 @@
+/*
+ * This file is part of Child Monitor.
+ *
+ * Child Monitor is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Child Monitor is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
+ */
+package de.rochefort.childmonitor
+
+import android.app.Notification
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.app.Service
+import android.content.Intent
+import android.content.pm.ServiceInfo
+import android.media.AudioRecord
+import android.media.MediaRecorder
+import android.net.nsd.NsdManager
+import android.net.nsd.NsdManager.RegistrationListener
+import android.net.nsd.NsdServiceInfo
+import android.os.Binder
+import android.os.Build
+import android.os.IBinder
+import android.util.Log
+import android.widget.TextView
+import android.widget.Toast
+import androidx.core.app.NotificationCompat
+import androidx.core.app.ServiceCompat
+import java.io.IOException
+import java.net.ServerSocket
+import java.net.Socket
+
+class MonitorService : Service() {
+    private val binder: IBinder = MonitorBinder()
+    private var nsdManager: NsdManager? = null
+    private var registrationListener: RegistrationListener? = null
+    private var currentSocket: ServerSocket? = null
+    private var connectionToken: Any? = null
+    private var currentPort = 0
+    private var notificationManager: NotificationManager? = null
+    private var monitorThread: Thread? = null
+    private var monitorActivity: MonitorActivity? = null
+    fun setMonitorActivity(monitorActivity: MonitorActivity?) {
+        this.monitorActivity = monitorActivity
+    }
+
+    private fun serviceConnection(socket: Socket) {
+        val ma = this.monitorActivity
+        ma?.runOnUiThread {
+            val statusText = ma.findViewById<TextView>(R.id.textStatus)
+            statusText.setText(R.string.streaming)
+        }
+        val frequency: Int = AudioCodecDefines.Companion.FREQUENCY
+        val channelConfiguration: Int = AudioCodecDefines.Companion.CHANNEL_CONFIGURATION_IN
+        val audioEncoding: Int = AudioCodecDefines.Companion.ENCODING
+        val bufferSize = AudioRecord.getMinBufferSize(frequency, channelConfiguration, audioEncoding)
+        val audioRecord: AudioRecord = try {
+            AudioRecord(
+                    MediaRecorder.AudioSource.MIC,
+                    frequency,
+                    channelConfiguration,
+                    audioEncoding,
+                    bufferSize
+            )
+        } catch (e: SecurityException) {
+            // This should never happen, we asked for permission before
+            throw RuntimeException(e)
+        }
+        val pcmBufferSize = bufferSize * 2
+        val pcmBuffer = ShortArray(pcmBufferSize)
+        val ulawBuffer = ByteArray(pcmBufferSize)
+        try {
+            audioRecord.startRecording()
+            val out = socket.getOutputStream()
+            socket.sendBufferSize = pcmBufferSize
+            Log.d(TAG, "Socket send buffer size: " + socket.sendBufferSize)
+            while (socket.isConnected && (this.currentSocket != null) && !Thread.currentThread().isInterrupted) {
+                val read = audioRecord.read(pcmBuffer, 0, bufferSize)
+                val encoded: Int = AudioCodecDefines.Companion.CODEC.encode(pcmBuffer, read, ulawBuffer, 0)
+                out.write(ulawBuffer, 0, encoded)
+            }
+        } catch (e: Exception) {
+            Log.e(TAG, "Connection failed", e)
+        } finally {
+            audioRecord.stop()
+        }
+    }
+
+    override fun onCreate() {
+        Log.i(TAG, "ChildMonitor start")
+        super.onCreate()
+        this.notificationManager = getSystemService(NOTIFICATION_SERVICE) as NotificationManager
+        this.nsdManager = this.getSystemService(NSD_SERVICE) as NsdManager
+        this.currentPort = 10000
+        this.currentSocket = null
+    }
+
+    override fun onStartCommand(intent: Intent, flags: Int, startId: Int): Int {
+        Log.i(TAG, "Received start id $startId: $intent")
+        // Display a notification about us starting.  We put an icon in the status bar.
+        createNotificationChannel()
+        val n = buildNotification()
+        val foregroundServiceType = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) ServiceInfo.FOREGROUND_SERVICE_TYPE_MICROPHONE else 0 // Keep the linter happy
+        ServiceCompat.startForeground(this, ID, n, foregroundServiceType)
+        ensureMonitorThread()
+        return START_REDELIVER_INTENT
+    }
+
+    private fun ensureMonitorThread() {
+        var mt = this.monitorThread
+        if (mt != null && mt.isAlive) {
+            return
+        }
+        val currentToken = Any()
+        this.connectionToken = currentToken
+        mt = Thread {
+            while (this.connectionToken == currentToken) {
+                try {
+                    ServerSocket(this.currentPort).use { serverSocket ->
+                        this.currentSocket = serverSocket
+                        // Store the chosen port.
+                        val localPort = serverSocket.localPort
+
+                        // Register the service so that parent devices can
+                        // locate the child device
+                        registerService(localPort)
+                        serverSocket.accept().use { socket ->
+                            Log.i(TAG, "Connection from parent device received")
+
+                            // We now have a client connection.
+                            // Unregister so no other clients will
+                            // attempt to connect
+                            unregisterService()
+                            serviceConnection(socket)
+                        }
+                    }
+                } catch (e: Exception) {
+                    if (this.connectionToken == currentToken) {
+                        // Just in case
+                        this.currentPort++
+                        Log.e(TAG, "Failed to open server socket. Port increased to $currentPort", e)
+                    }
+                }
+            }
+        }
+        this.monitorThread = mt
+        mt.start()
+    }
+
+    private fun registerService(port: Int) {
+        val serviceInfo = NsdServiceInfo()
+        serviceInfo.serviceName = "ChildMonitor on " + Build.MODEL
+        serviceInfo.serviceType = "_childmonitor._tcp."
+        serviceInfo.port = port
+        this.registrationListener = object : RegistrationListener {
+            override fun onServiceRegistered(nsdServiceInfo: NsdServiceInfo) {
+                // Save the service name.  Android may have changed it in order to
+                // resolve a conflict, so update the name you initially requested
+                // with the name Android actually used.
+                val serviceName = nsdServiceInfo.serviceName
+                Log.i(TAG, "Service name: $serviceName")
+                val ma = monitorActivity
+                ma?.runOnUiThread {
+                    val statusText = ma.findViewById<TextView>(R.id.textStatus)
+                    statusText.setText(R.string.waitingForParent)
+                    val serviceText = ma.findViewById<TextView>(R.id.textService)
+                    serviceText.text = serviceName
+                    val portText = ma.findViewById<TextView>(R.id.port)
+                    portText.text = Integer.toString(port)
+                }
+            }
+
+            override fun onRegistrationFailed(serviceInfo: NsdServiceInfo, errorCode: Int) {
+                // Registration failed!  Put debugging code here to determine why.
+                Log.e(TAG, "Registration failed: $errorCode")
+            }
+
+            override fun onServiceUnregistered(arg0: NsdServiceInfo) {
+                // Service has been unregistered.  This only happens when you call
+                // NsdManager.unregisterService() and pass in this listener.
+                Log.i(TAG, "Unregistering service")
+            }
+
+            override fun onUnregistrationFailed(serviceInfo: NsdServiceInfo, errorCode: Int) {
+                // Unregistration failed.  Put debugging code here to determine why.
+                Log.e(TAG, "Unregistration failed: $errorCode")
+            }
+        }
+        nsdManager!!.registerService(
+                serviceInfo, NsdManager.PROTOCOL_DNS_SD, registrationListener)
+    }
+
+    private fun unregisterService() {
+        val currentListener = this.registrationListener
+        if (currentListener != null) {
+            Log.i(TAG, "Unregistering monitoring service")
+            this.nsdManager!!.unregisterService(currentListener)
+            this.registrationListener = null
+        }
+    }
+
+    private fun createNotificationChannel() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            val serviceChannel = NotificationChannel(
+                    CHANNEL_ID,
+                    "Foreground Service Channel",
+                    NotificationManager.IMPORTANCE_DEFAULT
+            )
+            this.notificationManager!!.createNotificationChannel(serviceChannel)
+        }
+    }
+
+    private fun buildNotification(): Notification {
+        val text: CharSequence = "Child Device"
+        // Set the info for the views that show in the notification panel.
+        val b = NotificationCompat.Builder(this, CHANNEL_ID)
+        b.setSmallIcon(R.drawable.listening_notification) // the status icon
+                .setOngoing(true)
+                .setTicker(text) // the status text
+                .setContentTitle(text) // the label of the entry
+        return b.build()
+    }
+
+    override fun onDestroy() {
+        val mt = this.monitorThread
+        if (mt != null) {
+            mt.interrupt()
+            this.monitorThread = null
+        }
+        unregisterService()
+        this.connectionToken = null
+        val sock = this.currentSocket
+        if (sock != null) {
+            try {
+                sock.close()
+                this.currentSocket = null
+            } catch (e: IOException) {
+                Log.e(TAG, "Failed to close active socket on port $currentPort")
+            }
+        }
+
+        // Cancel the persistent notification.
+        this.notificationManager!!.cancel(R.string.listening)
+        ServiceCompat.stopForeground(this, ServiceCompat.STOP_FOREGROUND_REMOVE)
+        // Tell the user we stopped.
+        Toast.makeText(this, R.string.stopped, Toast.LENGTH_SHORT).show()
+        super.onDestroy()
+    }
+
+    override fun onBind(intent: Intent): IBinder {
+        return binder
+    }
+
+    inner class MonitorBinder : Binder() {
+        val service: MonitorService
+            get() = this@MonitorService
+    }
+
+    companion object {
+        const val TAG = "MonitorService"
+        const val CHANNEL_ID = TAG
+        const val ID = 1338
+    }
+}
diff --git a/app/src/main/java/de/rochefort/childmonitor/StartActivity.java b/app/src/main/java/de/rochefort/childmonitor/StartActivity.java
deleted file mode 100644
index a889e68..0000000
--- a/app/src/main/java/de/rochefort/childmonitor/StartActivity.java
+++ /dev/null
@@ -1,96 +0,0 @@
-/*
- * This file is part of Child Monitor.
- *
- * Child Monitor is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Child Monitor is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
- */
-package de.rochefort.childmonitor;
-
-import android.Manifest;
-import android.app.Activity;
-import android.content.Intent;
-import android.content.pm.PackageManager;
-import android.os.Bundle;
-import android.support.v4.app.ActivityCompat;
-import android.support.v4.content.ContextCompat;
-import android.util.Log;
-import android.widget.Button;
-
-public class StartActivity extends Activity {
-    static final String TAG = "ChildMonitor";
-    private final static int PERMISSIONS_REQUEST_RECORD_AUDIO = 298349824;
-    private final static int PERMISSIONS_REQUEST_MULTICAST = 298349825;
-
-    @Override
-    protected void onCreate(Bundle savedInstanceState) {
-        Log.i(TAG, "ChildMonitor launched");
-
-        super.onCreate(savedInstanceState);
-        setContentView(R.layout.activity_start);
-
-        final Button monitorButton = findViewById(R.id.useChildDevice);
-        monitorButton.setOnClickListener(v -> {
-            Log.i(TAG, "Starting up monitor");
-
-            if (isAudioRecordingPermissionGranted()) {
-                startActivity(new Intent(getApplicationContext(), MonitorActivity.class));
-            } else {
-                requestAudioPermission();
-            }
-        });
-
-        final Button connectButton = findViewById(R.id.useParentDevice);
-        connectButton.setOnClickListener(v -> {
-            Log.i(TAG, "Starting connection activity");
-            if (isMulticastPermissionGranted()) {
-                Intent i = new Intent(getApplicationContext(), DiscoverActivity.class);
-                startActivity(i);
-            } else {
-                requestMulticastPermission();
-            }
-        });
-    }
-
-    private boolean isMulticastPermissionGranted() {
-        return ContextCompat.checkSelfPermission(StartActivity.this, Manifest.permission.CHANGE_WIFI_MULTICAST_STATE)
-                == PackageManager.PERMISSION_GRANTED;
-    }
-
-    private boolean isAudioRecordingPermissionGranted() {
-        return ContextCompat.checkSelfPermission(StartActivity.this, Manifest.permission.RECORD_AUDIO)
-                == PackageManager.PERMISSION_GRANTED;
-    }
-
-    private void requestAudioPermission() {
-        ActivityCompat.requestPermissions(StartActivity.this,
-                new String[]{Manifest.permission.RECORD_AUDIO},
-                PERMISSIONS_REQUEST_RECORD_AUDIO);
-    }
-
-    private void requestMulticastPermission() {
-        ActivityCompat.requestPermissions(StartActivity.this,
-                new String[]{Manifest.permission.CHANGE_WIFI_MULTICAST_STATE},
-                PERMISSIONS_REQUEST_MULTICAST);
-    }
-
-    @Override
-    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
-        if (requestCode == PERMISSIONS_REQUEST_RECORD_AUDIO && grantResults.length > 0
-                && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
-            startActivity(new Intent(getApplicationContext(), MonitorActivity.class));
-        } else if (requestCode == PERMISSIONS_REQUEST_MULTICAST) {
-            // its okay if the permission was denied... the user will have to type the address manually
-            startActivity(new Intent(getApplicationContext(), DiscoverActivity.class));
-        }
-    }
-}
diff --git a/app/src/main/java/de/rochefort/childmonitor/StartActivity.kt b/app/src/main/java/de/rochefort/childmonitor/StartActivity.kt
new file mode 100644
index 0000000..fcc1ec3
--- /dev/null
+++ b/app/src/main/java/de/rochefort/childmonitor/StartActivity.kt
@@ -0,0 +1,87 @@
+/*
+ * This file is part of Child Monitor.
+ *
+ * Child Monitor is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Child Monitor is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
+ */
+package de.rochefort.childmonitor
+
+import android.Manifest
+import android.app.Activity
+import android.content.Intent
+import android.content.pm.PackageManager
+import android.os.Bundle
+import android.util.Log
+import android.view.View
+import android.widget.Button
+import androidx.core.app.ActivityCompat
+import androidx.core.content.ContextCompat
+
+class StartActivity : Activity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        Log.i(TAG, "ChildMonitor launched")
+        super.onCreate(savedInstanceState)
+        setContentView(R.layout.activity_start)
+        val monitorButton = findViewById<Button>(R.id.useChildDevice)
+        monitorButton.setOnClickListener { v: View? ->
+            Log.i(TAG, "Starting up monitor")
+            if (isAudioRecordingPermissionGranted) {
+                startActivity(Intent(applicationContext, MonitorActivity::class.java))
+            } else {
+                requestAudioPermission()
+            }
+        }
+        val connectButton = findViewById<Button>(R.id.useParentDevice)
+        connectButton.setOnClickListener { v: View? ->
+            Log.i(TAG, "Starting connection activity")
+            if (isMulticastPermissionGranted) {
+                val i = Intent(applicationContext, DiscoverActivity::class.java)
+                startActivity(i)
+            } else {
+                requestMulticastPermission()
+            }
+        }
+    }
+
+    private val isMulticastPermissionGranted: Boolean
+        get() = (ContextCompat.checkSelfPermission(this@StartActivity, Manifest.permission.CHANGE_WIFI_MULTICAST_STATE)
+                == PackageManager.PERMISSION_GRANTED)
+    private val isAudioRecordingPermissionGranted: Boolean
+        get() = (ContextCompat.checkSelfPermission(this@StartActivity, Manifest.permission.RECORD_AUDIO)
+                == PackageManager.PERMISSION_GRANTED)
+
+    private fun requestAudioPermission() {
+        ActivityCompat.requestPermissions(this@StartActivity, arrayOf(Manifest.permission.RECORD_AUDIO),
+                PERMISSIONS_REQUEST_RECORD_AUDIO)
+    }
+
+    private fun requestMulticastPermission() {
+        ActivityCompat.requestPermissions(this@StartActivity, arrayOf(Manifest.permission.CHANGE_WIFI_MULTICAST_STATE),
+                PERMISSIONS_REQUEST_MULTICAST)
+    }
+
+    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<String>, grantResults: IntArray) {
+        if (requestCode == PERMISSIONS_REQUEST_RECORD_AUDIO && grantResults.size > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
+            startActivity(Intent(applicationContext, MonitorActivity::class.java))
+        } else if (requestCode == PERMISSIONS_REQUEST_MULTICAST) {
+            // its okay if the permission was denied... the user will have to type the address manually
+            startActivity(Intent(applicationContext, DiscoverActivity::class.java))
+        }
+    }
+
+    companion object {
+        const val TAG = "ChildMonitor"
+        private const val PERMISSIONS_REQUEST_RECORD_AUDIO = 298349824
+        private const val PERMISSIONS_REQUEST_MULTICAST = 298349825
+    }
+}
diff --git a/app/src/main/java/de/rochefort/childmonitor/VolumeHistory.java b/app/src/main/java/de/rochefort/childmonitor/VolumeHistory.java
deleted file mode 100644
index 6295a9c..0000000
--- a/app/src/main/java/de/rochefort/childmonitor/VolumeHistory.java
+++ /dev/null
@@ -1,77 +0,0 @@
-/*
- * This file is part of Child Monitor.
- *
- * Child Monitor is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Child Monitor is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
- */
-package de.rochefort.childmonitor;
-
-import android.os.Handler;
-import android.os.Looper;
-import android.support.v4.util.CircularArray;
-
-public class VolumeHistory {
-    private double maxVolume = 0.25;
-
-    private double volumeNorm = 1.0 / maxVolume;
-    private final CircularArray<Double> historyData;
-    private final int maxHistory;
-
-    private final Handler uiHandler;
-
-    VolumeHistory(int maxHistory) {
-        uiHandler = new Handler(Looper.getMainLooper());
-        this.maxHistory = maxHistory;
-        historyData = new CircularArray<>(maxHistory);
-    }
-
-
-    public double getVolumeNorm() {
-        return volumeNorm;
-    }
-
-    public double get(int i) {
-        return historyData.get(i);
-    }
-
-    public int size() {
-        return historyData.size();
-    }
-
-    private void addLast(double volume) {
-        // schedule editing of member vars on the ui event loop to avoid concurrency problems
-        uiHandler.post(() -> {
-            if (volume > maxVolume) {
-                maxVolume = volume;
-                volumeNorm = 1.0 / volume;
-            }
-            historyData.addLast(volume);
-            historyData.removeFromStart(historyData.size() - maxHistory);
-        });
-    }
-
-    public void onAudioData(short[] data) {
-        if (data.length < 1) {
-            return;
-        }
-
-        final double scale = 1.0 / 128.0;
-        double sum = 0;
-        for (final short datum : data) {
-            final double rel = datum * scale;
-            sum += rel * rel;
-        }
-        final double volume = sum / data.length;
-        addLast(volume);
-    }
-}
diff --git a/app/src/main/java/de/rochefort/childmonitor/VolumeHistory.kt b/app/src/main/java/de/rochefort/childmonitor/VolumeHistory.kt
new file mode 100644
index 0000000..8ee200d
--- /dev/null
+++ b/app/src/main/java/de/rochefort/childmonitor/VolumeHistory.kt
@@ -0,0 +1,63 @@
+/*
+ * This file is part of Child Monitor.
+ *
+ * Child Monitor is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Child Monitor is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
+ */
+package de.rochefort.childmonitor
+
+import android.os.Handler
+import android.os.Looper
+import androidx.collection.CircularArray
+
+class VolumeHistory internal constructor(private val maxHistory: Int) {
+    private var maxVolume = 0.25
+    var volumeNorm = 1.0 / this.maxVolume
+        private set
+    private val historyData: CircularArray<Double> = CircularArray(maxHistory)
+    private val uiHandler: Handler = Handler(Looper.getMainLooper())
+
+    operator fun get(i: Int): Double {
+        return historyData[i]
+    }
+
+    fun size(): Int {
+        return historyData.size()
+    }
+
+    private fun addLast(volume: Double) {
+        // schedule editing of member vars on the ui event loop to avoid concurrency problems
+        uiHandler.post {
+            if (volume > this.maxVolume) {
+                this.maxVolume = volume
+                this.volumeNorm = 1.0 / volume
+            }
+            historyData.addLast(volume)
+            historyData.removeFromStart(historyData.size() - maxHistory)
+        }
+    }
+
+    fun onAudioData(data: ShortArray) {
+        if (data.isEmpty()) {
+            return
+        }
+        val scale = 1.0 / 128.0
+        var sum = 0.0
+        for (datum in data) {
+            val rel = datum * scale
+            sum += rel * rel
+        }
+        val volume = sum / data.size
+        addLast(volume)
+    }
+}
diff --git a/app/src/main/java/de/rochefort/childmonitor/VolumeView.java b/app/src/main/java/de/rochefort/childmonitor/VolumeView.java
deleted file mode 100644
index cf3c448..0000000
--- a/app/src/main/java/de/rochefort/childmonitor/VolumeView.java
+++ /dev/null
@@ -1,104 +0,0 @@
-/*
- * This file is part of Child Monitor.
- *
- * Child Monitor is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Child Monitor is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
- */
-package de.rochefort.childmonitor;
-
-import android.content.Context;
-import android.graphics.Canvas;
-import android.graphics.Color;
-import android.graphics.Paint;
-import android.support.annotation.Nullable;
-import android.util.AttributeSet;
-import android.view.View;
-
-public class VolumeView extends View {
-    private final Paint paint;
-    private VolumeHistory volumeHistory;
-
-    public VolumeView(Context context) {
-        super(context);
-        this.paint = initPaint();
-    }
-
-    public VolumeView(Context context, @Nullable AttributeSet attrs) {
-        super(context, attrs);
-        this.paint = initPaint();
-    }
-
-    public VolumeView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
-        super(context, attrs, defStyleAttr);
-        this.paint = initPaint();
-    }
-
-    private Paint initPaint() {
-        Paint paint = new Paint();
-        paint.setColor(Color.rgb(255, 127, 0));
-        return paint;
-    }
-
-    @Override
-    protected void onDraw(Canvas canvas) {
-        final VolumeHistory volumeHistory = this.volumeHistory;
-        if (volumeHistory == null) {
-            return;
-        }
-
-        final int height = getHeight();
-        final int width = getWidth();
-
-        final int size = volumeHistory.size();    // Size is at most width
-        final double volumeNorm = volumeHistory.getVolumeNorm();
-        final double relativeBrightness;
-        if (size > 0) {
-            final double normalizedVolume = volumeHistory.get(size - 1);
-            relativeBrightness = Math.max(0.3, normalizedVolume);
-        } else {
-            relativeBrightness = 0.3;
-        }
-        int blue;
-        int rest;
-        if (relativeBrightness > 0.5) {
-            blue = 255;
-            rest = (int) (2 * 255 * (relativeBrightness - 0.5));
-        } else {
-            blue = (int) (255 * (relativeBrightness - 0.2) / 0.3);
-            rest = 0;
-        }
-        final int rgb = Color.rgb(rest, rest, blue);
-        canvas.drawColor(rgb);
-        if (size == 0) {
-            return;
-        }
-        final double margins = height * 0.1;
-        final double graphHeight = height - 2.0 * margins;
-        int leftMost = Math.max(0, volumeHistory.size() - width);
-        final double graphScale = graphHeight * volumeNorm;
-
-        int xPrev = 0;
-        int yPrev = ((int) (margins + graphHeight - volumeHistory.get(leftMost) * graphScale));
-        int length = Math.min(size, width);
-        for (int xNext = 1; xNext < length-1; ++xNext) {
-            int yNext = (int) (margins + graphHeight - volumeHistory.get(leftMost + xNext) * graphScale);
-            canvas.drawLine(xPrev, yPrev, xNext, yNext, paint);
-            xPrev = xNext;
-            yPrev = yNext;
-        }
-    }
-
-    public void setVolumeHistory(VolumeHistory volumeHistory) {
-        this.volumeHistory = volumeHistory;
-    }
-}
diff --git a/app/src/main/java/de/rochefort/childmonitor/VolumeView.kt b/app/src/main/java/de/rochefort/childmonitor/VolumeView.kt
new file mode 100644
index 0000000..2d23df8
--- /dev/null
+++ b/app/src/main/java/de/rochefort/childmonitor/VolumeView.kt
@@ -0,0 +1,92 @@
+/*
+ * This file is part of Child Monitor.
+ *
+ * Child Monitor is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Child Monitor is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Child Monitor. If not, see <http://www.gnu.org/licenses/>.
+ */
+package de.rochefort.childmonitor
+
+import android.content.Context
+import android.graphics.Canvas
+import android.graphics.Color
+import android.graphics.Paint
+import android.util.AttributeSet
+import android.view.View
+
+class VolumeView : View {
+    private val paint: Paint
+    private var volumeHistory: VolumeHistory? = null
+
+    constructor(context: Context?) : super(context) {
+        paint = initPaint()
+    }
+
+    constructor(context: Context?, attrs: AttributeSet?) : super(context, attrs) {
+        paint = initPaint()
+    }
+
+    constructor(context: Context?, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr) {
+        paint = initPaint()
+    }
+
+    private fun initPaint(): Paint {
+        val paint = Paint()
+        paint.color = Color.rgb(255, 127, 0)
+        return paint
+    }
+
+    override fun onDraw(canvas: Canvas) {
+        val volumeHistory = this.volumeHistory ?: return
+        val height = height
+        val width = width
+        val size = volumeHistory.size() // Size is at most width
+        val volumeNorm = volumeHistory.volumeNorm
+        val relativeBrightness: Double = if (size > 0) {
+            val normalizedVolume = volumeHistory[size - 1]
+            Math.max(0.3, normalizedVolume)
+        } else {
+            0.3
+        }
+        val blue: Int
+        val rest: Int
+        if (relativeBrightness > 0.5) {
+            blue = 255
+            rest = (2 * 255 * (relativeBrightness - 0.5)).toInt()
+        } else {
+            blue = (255 * (relativeBrightness - 0.2) / 0.3).toInt()
+            rest = 0
+        }
+        val rgb = Color.rgb(rest, rest, blue)
+        canvas.drawColor(rgb)
+        if (size == 0) {
+            return
+        }
+        val margins = height * 0.1
+        val graphHeight = height - 2.0 * margins
+        val leftMost = Math.max(0, volumeHistory.size() - width)
+        val graphScale = graphHeight * volumeNorm
+        var xPrev = 0
+        var yPrev = (margins + graphHeight - volumeHistory[leftMost] * graphScale).toInt()
+        val length = Math.min(size, width)
+        for (xNext in 1 until length - 1) {
+            val yNext = (margins + graphHeight - volumeHistory[leftMost + xNext] * graphScale).toInt()
+            canvas.drawLine(xPrev.toFloat(), yPrev.toFloat(), xNext.toFloat(), yNext.toFloat(), paint)
+            xPrev = xNext
+            yPrev = yNext
+        }
+    }
+
+    fun setVolumeHistory(volumeHistory: VolumeHistory?) {
+        this.volumeHistory = volumeHistory
+    }
+}
diff --git a/app/src/main/java/de/rochefort/childmonitor/audio/G711UCodec.java b/app/src/main/java/de/rochefort/childmonitor/audio/G711UCodec.java
deleted file mode 100644
index 8736a57..0000000
--- a/app/src/main/java/de/rochefort/childmonitor/audio/G711UCodec.java
+++ /dev/null
@@ -1,71 +0,0 @@
-/*
- * Copyright (C) 2009 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- *
- * Taken from https://android.googlesource.com/platform/external/nist-sip/+/6f95fdeab4481188b6260041b41d1db12b101266/src/com/android/sip/media/G711UCodec.java
- *
- */
-package de.rochefort.childmonitor.audio;
-/**
- * G.711 codec. This class provides u-law conversion.
- */
-public class G711UCodec {
-    // s00000001wxyz...s000wxyz
-    // s0000001wxyza...s001wxyz
-    // s000001wxyzab...s010wxyz
-    // s00001wxyzabc...s011wxyz
-    // s0001wxyzabcd...s100wxyz
-    // s001wxyzabcde...s101wxyz
-    // s01wxyzabcdef...s110wxyz
-    // s1wxyzabcdefg...s111wxyz
-    private static final byte[] table13to8 = new byte[8192];
-    private static final short[] table8to16 = new short[256];
-    static {
-        // b13 --> b8
-        for (int p = 1, q = 0; p <= 0x80; p <<= 1, q+=0x10) {
-            for (int i = 0, j = (p << 4) - 0x10; i < 16; i++, j += p) {
-                int v = (i + q) ^ 0x7F;
-                byte value1 = (byte) v;
-                byte value2 = (byte) (v + 128);
-                for (int m = j, e = j + p; m < e; m++) {
-                    table13to8[m] = value1;
-                    table13to8[8191 - m] = value2;
-                }
-            }
-        }
-        // b8 --> b16
-        for (int q = 0; q <= 7; q++) {
-            for (int i = 0, m = (q << 4); i < 16; i++, m++) {
-                int v = (((i + 0x10) << q) - 0x10) << 3;
-                table8to16[m ^ 0x7F] = (short) v;
-                table8to16[(m ^ 0x7F) + 128] = (short) (65536 - v);
-            }
-        }
-    }
-    public int decode(short[] b16, byte[] ulaw, int count, int offset) {
-        for (int i = 0, j = offset; i < count; i++, j++) {
-            b16[i] = table8to16[ulaw[j] & 0xFF];
-        }
-        return count;
-    }
-    public int encode(short[] b16, int count, byte[] b8, int offset) {
-        for (int i = 0, j = offset; i < count; i++, j++) {
-            b8[j] = table13to8[(b16[i] >> 4) & 0x1FFF];
-        }
-        return count;
-    }
-    public int getSampleCount(int frameSize) {
-        return frameSize;
-    }
-}
\ No newline at end of file
diff --git a/app/src/main/java/de/rochefort/childmonitor/audio/G711UCodec.kt b/app/src/main/java/de/rochefort/childmonitor/audio/G711UCodec.kt
new file mode 100644
index 0000000..86be4da
--- /dev/null
+++ b/app/src/main/java/de/rochefort/childmonitor/audio/G711UCodec.kt
@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Taken from https://android.googlesource.com/platform/external/nist-sip/+/6f95fdeab4481188b6260041b41d1db12b101266/src/com/android/sip/media/G711UCodec.java
+ *
+ */
+package de.rochefort.childmonitor.audio
+
+/**
+ * G.711 codec. This class provides u-law conversion.
+ */
+class G711UCodec {
+    fun decode(b16: ShortArray, ulaw: ByteArray, count: Int, offset: Int): Int {
+        var i = 0
+        var j = offset
+        while (i < count) {
+            b16[i] = table8to16[ulaw[j].toInt() and 0xFF]
+            i++
+            j++
+        }
+        return count
+    }
+
+    fun encode(b16: ShortArray, count: Int, b8: ByteArray, offset: Int): Int {
+        var i = 0
+        var j = offset
+        while (i < count) {
+            b8[j] = table13to8[b16[i].toInt() shr 4 and 0x1FFF]
+            i++
+            j++
+        }
+        return count
+    }
+
+    fun getSampleCount(frameSize: Int): Int {
+        return frameSize
+    }
+
+    companion object {
+        // s00000001wxyz...s000wxyz
+        // s0000001wxyza...s001wxyz
+        // s000001wxyzab...s010wxyz
+        // s00001wxyzabc...s011wxyz
+        // s0001wxyzabcd...s100wxyz
+        // s001wxyzabcde...s101wxyz
+        // s01wxyzabcdef...s110wxyz
+        // s1wxyzabcdefg...s111wxyz
+        private val table13to8 = ByteArray(8192)
+        private val table8to16 = ShortArray(256)
+
+        init {
+            // b13 --> b8
+            run {
+                var p = 1
+                var q = 0
+                while (p <= 0x80) {
+                    var i = 0
+                    var j = (p shl 4) - 0x10
+                    while (i < 16) {
+                        val v = i + q xor 0x7F
+                        val value1 = v.toByte()
+                        val value2 = (v + 128).toByte()
+                        var m = j
+                        val e = j + p
+                        while (m < e) {
+                            table13to8[m] = value1
+                            table13to8[8191 - m] = value2
+                            m++
+                        }
+                        i++
+                        j += p
+                    }
+                    p = p shl 1
+                    q += 0x10
+                }
+            }
+            // b8 --> b16
+            for (q in 0..7) {
+                var i = 0
+                var m = q shl 4
+                while (i < 16) {
+                    val v = (i + 0x10 shl q) - 0x10 shl 3
+                    table8to16[m xor 0x7F] = v.toShort()
+                    table8to16[(m xor 0x7F) + 128] = (65536 - v).toShort()
+                    i++
+                    m++
+                }
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/build.gradle b/build.gradle
index dcfffc8..3e8cfeb 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,17 +1,44 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 buildscript {
+    ext {
+        kotlin_version = '1.9.22'
+    }
     repositories {
         mavenCentral()
         google()
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:8.2.2'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
     }
 }
 
+plugins {
+    id 'org.jetbrains.kotlin.jvm' version '1.9.22'
+}
+
 allprojects {
     repositories {
         mavenCentral()
         google()
     }
 }
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
+}
+
+compileKotlin {
+    kotlinOptions {
+        jvmTarget = "17"
+    }
+}
+compileTestKotlin {
+    kotlinOptions {
+        jvmTarget = "17"
+    }
+}
diff --git a/gradle.properties b/gradle.properties
index 6436ed6..5d1e40b 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -20,6 +20,8 @@
 # The aapt2 tool creates an APK which fails to install on Android 5 and below if it contains
 # a bug. Build tools 27.0.1 has a mitigation. Avoiding aapt2 also avoids hitting the bug.
 # See: https://issuetracker.google.com/issues/64434571
+android.enableJetifier=false
 android.nonFinalResIds=false
 android.nonTransitiveRClass=true
+android.useAndroidX=true
 org.gradle.configuration-cache=true
\ No newline at end of file
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index 6715352..1910e5d 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -1,7 +1,7 @@
-#Tue Apr 14 20:27:54 CEST 2020
+#Sun Feb 18 21:28:01 CET 2024
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
+distributionSha256Sum=9631d53cf3e74bfa726893aee1f8994fee4e060c401335946dba2156f440f24c
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.6-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.2.1-all.zip
-distributionSha256Sum=7c3ad722e9b0ce8205b91560fd6ce8296ac3eadf065672242fd73c06b8eeb6ee