diff --git a/app/src/main/java/de/ccc/events/badge/card10/Constants.kt b/app/src/main/java/de/ccc/events/badge/card10/Constants.kt
index 6abb6f8ad80da8e2de427dd7706314ad5ecf7d63..c69454e7f3410cbe81f04e98a49e80ea5828282a 100644
--- a/app/src/main/java/de/ccc/events/badge/card10/Constants.kt
+++ b/app/src/main/java/de/ccc/events/badge/card10/Constants.kt
@@ -24,6 +24,8 @@ package de.ccc.events.badge.card10
 
 import java.util.*
 
+const val CARD10_BLUETOOTH_MAC_PREFIX = "CA:4D:10"
+
 val GENERIC_ACCESS_SERVICE_UUID = UUID.fromString("00001800-0000-1000-8000-00805f9b34fb")
 val DEVICE_NAME_CHARACTERISTIC_UUID = UUID.fromString("00002a00-0000-1000-8000-00805f9b34fb")
 
diff --git a/app/src/main/java/de/ccc/events/badge/card10/background/UpdateClockJob.kt b/app/src/main/java/de/ccc/events/badge/card10/background/UpdateClockJob.kt
index e3e655a108cdcafb47ea714bb1aa7cb8a977995c..ea34deb1f045829b27080549dd721560bcc4805e 100644
--- a/app/src/main/java/de/ccc/events/badge/card10/background/UpdateClockJob.kt
+++ b/app/src/main/java/de/ccc/events/badge/card10/background/UpdateClockJob.kt
@@ -29,6 +29,7 @@ import android.bluetooth.BluetoothGattCharacteristic
 import android.content.Context
 import androidx.work.Worker
 import androidx.work.WorkerParameters
+import de.ccc.events.badge.card10.CARD10_BLUETOOTH_MAC_PREFIX
 import de.ccc.events.badge.card10.CARD10_SERVICE_UUID
 import de.ccc.events.badge.card10.TIME_CHARACTERISTIC_UUID
 import java.nio.ByteBuffer
@@ -41,55 +42,57 @@ class UpdateClockJob(context: Context, workerParameters: WorkerParameters) : Wor
     override fun doWork(): Result {
         System.out.println("=== doWork() job started")
         for (device in bluetoothAdapter.bondedDevices) {
-            System.out.println("=== doWork() ${device}")
-            var gatt: BluetoothGatt? = null
-            try {
-                val gattLatch = CountDownLatch(1);
-                var writeLatch: CountDownLatch? = null
-                var timeCharacteristic: BluetoothGattCharacteristic? = null
-                val callback = object : BluetoothGattCallback() {
-                    override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {
-                        System.out.println("=== doWork() onConnectionStateChange " + gatt + " / " + status + " / " + newState)
-                        if (newState == BluetoothGatt.STATE_CONNECTED)
-                            gatt.discoverServices()
-                    }
+            if (device.address.startsWith(CARD10_BLUETOOTH_MAC_PREFIX, true)) {
+                System.out.println("=== doWork() ${device}")
+                var gatt: BluetoothGatt? = null
+                try {
+                    val gattLatch = CountDownLatch(1);
+                    var writeLatch: CountDownLatch? = null
+                    var timeCharacteristic: BluetoothGattCharacteristic? = null
+                    val callback = object : BluetoothGattCallback() {
+                        override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {
+                            System.out.println("=== doWork() onConnectionStateChange " + gatt + " / " + status + " / " + newState)
+                            if (newState == BluetoothGatt.STATE_CONNECTED)
+                                gatt.discoverServices()
+                        }
 
-                    override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {
-                        System.out.println("=== doWork() onServicesDiscovered " + gatt + " / " + status)
-                        val card10Service = gatt.getService(CARD10_SERVICE_UUID)
-                        timeCharacteristic = card10Service.getCharacteristic(TIME_CHARACTERISTIC_UUID)
-                        gattLatch.countDown()
-                    }
+                        override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {
+                            System.out.println("=== doWork() onServicesDiscovered " + gatt + " / " + status)
+                            val card10Service = gatt.getService(CARD10_SERVICE_UUID)
+                            timeCharacteristic = card10Service.getCharacteristic(TIME_CHARACTERISTIC_UUID)
+                            gattLatch.countDown()
+                        }
 
-                    override fun onCharacteristicWrite(
-                        gatt: BluetoothGatt?,
-                        characteristic: BluetoothGattCharacteristic?,
-                        status: Int
-                    ) {
-                        writeLatch?.countDown()
+                        override fun onCharacteristicWrite(
+                            gatt: BluetoothGatt?,
+                            characteristic: BluetoothGattCharacteristic?,
+                            status: Int
+                        ) {
+                            writeLatch?.countDown()
+                        }
                     }
-                }
-                gatt = device.connectGatt(applicationContext, true, callback)
-                if (!gattLatch.await(1, TimeUnit.MINUTES))
-                    return Result.retry()
+                    gatt = device.connectGatt(applicationContext, true, callback)
+                    if (!gattLatch.await(1, TimeUnit.MINUTES))
+                        return Result.retry()
 
-                val buffer = ByteBuffer.allocate(8)
-                buffer.putLong(System.currentTimeMillis())
-                timeCharacteristic?.value = buffer.array()
-                if (gatt.writeCharacteristic(timeCharacteristic)) {
-                    writeLatch = CountDownLatch(1)
-                    if (!writeLatch.await(1, TimeUnit.MINUTES))
-                        return Result.failure()
-                    System.out.println("=== doWork() updated time")
+                    val buffer = ByteBuffer.allocate(8)
+                    buffer.putLong(System.currentTimeMillis())
+                    timeCharacteristic?.value = buffer.array()
+                    if (gatt.writeCharacteristic(timeCharacteristic)) {
+                        writeLatch = CountDownLatch(1)
+                        if (!writeLatch.await(1, TimeUnit.MINUTES))
+                            return Result.failure()
+                        System.out.println("=== doWork() updated time")
+                    }
+                } catch (x: Exception) {
+                    x.printStackTrace()
+                } finally {
+                    gatt?.close();
                 }
-            } catch (x: Exception) {
-                x.printStackTrace()
-            } finally {
-                gatt?.close();
-                System.out.println("=== doWork() job finished")
             }
         }
 
+        System.out.println("=== doWork() job finished (success)")
         return Result.success()
     }
 }
diff --git a/app/src/main/java/de/ccc/events/badge/card10/mood/MoodFragment.kt b/app/src/main/java/de/ccc/events/badge/card10/mood/MoodFragment.kt
index cde86d42cb7ed85140e70f74d53af0be87472d89..c55e75a9a9b5fb6e133bd88150cea0e8fe74248a 100644
--- a/app/src/main/java/de/ccc/events/badge/card10/mood/MoodFragment.kt
+++ b/app/src/main/java/de/ccc/events/badge/card10/mood/MoodFragment.kt
@@ -40,7 +40,7 @@ import java.util.concurrent.CountDownLatch
 class MoodFragment : Fragment() {
 
     // TODO pick from list of paired card10s, possibly present selection
-    private val REMOTE_DEVICE_BLUETOOTH_MAC = "00:05:8B:44:02:03"
+    private val REMOTE_DEVICE_BLUETOOTH_MAC = "CA:4D:10:44:02:03"
 
     private lateinit var gatt: BluetoothGatt
     private var rocketsCharacteristic: BluetoothGattCharacteristic? = null
diff --git a/app/src/main/java/de/ccc/events/badge/card10/scanner/ScannerFragment.kt b/app/src/main/java/de/ccc/events/badge/card10/scanner/ScannerFragment.kt
index 21ec56b6438a317e707717e66b5952d2a84415cb..8721fb046dbefa3d87dcf79ef0318497993e0f41 100644
--- a/app/src/main/java/de/ccc/events/badge/card10/scanner/ScannerFragment.kt
+++ b/app/src/main/java/de/ccc/events/badge/card10/scanner/ScannerFragment.kt
@@ -36,6 +36,7 @@ import android.view.View
 import android.view.ViewGroup
 import androidx.fragment.app.Fragment
 import androidx.recyclerview.widget.LinearLayoutManager
+import de.ccc.events.badge.card10.CARD10_BLUETOOTH_MAC_PREFIX
 import de.ccc.events.badge.card10.R
 import kotlinx.android.synthetic.main.scanner_fragment.*
 
@@ -47,15 +48,15 @@ class ScannerFragment : Fragment() {
     val callback = object : ScanCallback() {
         override fun onScanResult(callbackType: Int, result: ScanResult) {
             val device = result.device
-            if (device.name == null)
-                return
-            listAdapter.put(
-                Device(
-                    btMac = device.address,
-                    name = device.name,
-                    paired = device.bondState == BluetoothDevice.BOND_BONDED
+            if (device.address.startsWith(CARD10_BLUETOOTH_MAC_PREFIX, true)) {
+                listAdapter.put(
+                    Device(
+                        btMac = device.address,
+                        name = device.name,
+                        paired = device.bondState == BluetoothDevice.BOND_BONDED
+                    )
                 )
-            )
+            }
         }
     }