diff --git a/android/app/src/main/AndroidManifest.xml b/android/app/src/main/AndroidManifest.xml
index 9f0519d..ccabb3c 100644
--- a/android/app/src/main/AndroidManifest.xml
+++ b/android/app/src/main/AndroidManifest.xml
@@ -5,7 +5,8 @@
     <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" android:maxSdkVersion="30"/>
     <uses-permission android:name="android.permission.BLUETOOTH_SCAN"/>
     <uses-permission android:name="android.permission.BLUETOOTH_CONNECT"/>
-    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
+    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" android:maxSdkVersion="30" />
+    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" android:maxSdkVersion="30" />
 
     <uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>
     <uses-feature android:name="android.hardware.usb.host" android:required="false"/>
diff --git a/android/app/src/main/java/com/eddy/atomrelay/BleRelayManager.kt b/android/app/src/main/java/com/eddy/atomrelay/BleRelayManager.kt
index 15fdeb1..2f3dbae 100644
--- a/android/app/src/main/java/com/eddy/atomrelay/BleRelayManager.kt
+++ b/android/app/src/main/java/com/eddy/atomrelay/BleRelayManager.kt
@@ -40,6 +40,7 @@ class BleRelayManager(
         private const val MAX_SCAN_RETRIES = 3
         private const val HMAC_PKT_SIZE = 37
         private const val HMAC_LEN = 32
+        private const val BLE_MTU = 256
     }
 
     private var bluetoothGatt: BluetoothGatt? = null
@@ -55,6 +56,7 @@ class BleRelayManager(
     private val scanRunnable = Runnable { startScan() }
     private var scanTimeoutRunnable: Runnable? = null
 
+    @SuppressLint("MissingPermission")
     private val scanCallback = object : ScanCallback() {
         override fun onScanResult(callbackType: Int, result: ScanResult) {
             val device = result.device ?: return
@@ -139,6 +141,7 @@ class BleRelayManager(
         }
     }
 
+    @SuppressLint("MissingPermission")
     fun destroy() {
         handler.removeCallbacksAndMessages(null)
         stopScan()
@@ -220,7 +223,7 @@ class BleRelayManager(
                 return
             }
             Log.d(TAG, "Services discovered, requesting MTU...")
-            gatt.requestMtu(256)
+            gatt.requestMtu(BLE_MTU)
         }
 
         @SuppressLint("MissingPermission")
diff --git a/android/app/src/main/java/com/eddy/atomrelay/EspFlasher.kt b/android/app/src/main/java/com/eddy/atomrelay/EspFlasher.kt
index 8c7704a..ba3377b 100644
--- a/android/app/src/main/java/com/eddy/atomrelay/EspFlasher.kt
+++ b/android/app/src/main/java/com/eddy/atomrelay/EspFlasher.kt
@@ -18,6 +18,10 @@ class EspFlasher(private val context: Context) {
 
     companion object {
         private const val TAG = "EspFlasher"
+        private const val USB_SETTLE_MS = 500L
+        private const val KB = 1024
+        private const val FLASH_RESET_PCT = 95
+        private const val FLASH_DONE_PCT = 100
     }
 
     interface FlashCallback {
@@ -48,7 +52,7 @@ class EspFlasher(private val context: Context) {
     )
 
     private suspend fun doFlash(usbManager: UsbManager, device: UsbDevice, callback: FlashCallback) {
-        kotlinx.coroutines.delay(500)
+        kotlinx.coroutines.delay(USB_SETTLE_MS)
         coroutineContext.ensureActive()
 
         val connection = usbManager.openDevice(device)
@@ -108,20 +112,20 @@ class EspFlasher(private val context: Context) {
             for (step in steps) {
                 coroutineContext.ensureActive()
                 val stepName = context.getString(step.nameResId)
-                val sizeStr = if (step.data.size > 1024) "${step.data.size / 1024}KB" else "${step.data.size} bytes"
-                callback.onProgress(step.baseProgress, "$stepName schrijven ($sizeStr)...")
+                val sizeStr = if (step.data.size > KB) "${step.data.size / KB}KB" else "${step.data.size} bytes"
+                callback.onProgress(step.baseProgress, context.getString(R.string.flash_writing, stepName, sizeStr))
 
                 val writeStub = if (step.compress) stub.withCompression(true) else stub.withCompression(false)
                 writeStub.writeFlash(step.address, step.data)
 
                 val endProgress = step.baseProgress + step.range
-                callback.onProgress(endProgress.coerceAtMost(95), "$stepName geschreven")
+                callback.onProgress(endProgress.coerceAtMost(FLASH_RESET_PCT), context.getString(R.string.flash_written, stepName))
             }
 
-            callback.onProgress(95, "ESP resetten...")
+            callback.onProgress(FLASH_RESET_PCT, context.getString(R.string.flash_resetting))
             stub.reset()
 
-            callback.onProgress(100, context.getString(R.string.flash_done))
+            callback.onProgress(FLASH_DONE_PCT, context.getString(R.string.flash_done))
         } finally {
             connection.close()
         }
diff --git a/android/app/src/main/java/com/eddy/atomrelay/SettingsActivity.kt b/android/app/src/main/java/com/eddy/atomrelay/SettingsActivity.kt
index fc4895e..e1946e1 100644
--- a/android/app/src/main/java/com/eddy/atomrelay/SettingsActivity.kt
+++ b/android/app/src/main/java/com/eddy/atomrelay/SettingsActivity.kt
@@ -55,6 +55,11 @@ class SettingsActivity : AppCompatActivity() {
         private const val ACTION_USB_PERMISSION = "com.eddy.atomrelay.USB_PERMISSION"
         private const val STYLE_SPINNER = 0
         private const val STYLE_HORIZONTAL = 1
+        private const val USB_READ_BUF_SIZE = 512
+        private const val HMAC_HEX_LEN = 64
+        private const val UUID_HEX_LEN = 32
+        private const val UUID_BYTE_COUNT = 16
+        private const val HMAC_BYTE_COUNT = 32
     }
 
     private enum class UsbAction { NONE, EXCHANGE_KEY, FLASH }
@@ -480,8 +485,8 @@ class SettingsActivity : AppCompatActivity() {
                 if (keyLine != null && uuidLine != null) {
                     val hexKey = keyLine.removePrefix("HMAC_KEY:").trim()
                     val hexUuid = uuidLine.removePrefix("DEVICE_ID:").trim()
-                    if (hexKey.length == 64 && hexKey.all { it in "0123456789ABCDEFabcdef" } &&
-                        hexUuid.length == 32 && hexUuid.all { it in "0123456789ABCDEFabcdef" }) {
+                    if (hexKey.length == HMAC_HEX_LEN && hexKey.all { it in "0123456789ABCDEFabcdef" } &&
+                        hexUuid.length == UUID_HEX_LEN && hexUuid.all { it in "0123456789ABCDEFabcdef" }) {
                         val espKeyUpper = hexKey.uppercase()
                         val espUuidUpper = hexUuid.uppercase()
                         if (appUuid != null && appKey != null &&
@@ -502,7 +507,7 @@ class SettingsActivity : AppCompatActivity() {
                     } else {
                         Log.d(TAG, "Both have no keys, generating new pair")
                         newKey = generateRandomHexKey()
-                        newUuid = generateRandomHex(16)
+                        newUuid = generateRandomHex(UUID_BYTE_COUNT)
                     }
 
                     val setKeyCmd = "SET_KEY:$newKey\n".toByteArray(StandardCharsets.US_ASCII)
@@ -551,7 +556,7 @@ class SettingsActivity : AppCompatActivity() {
     }
 
     private fun flushReadBuffer(connection: UsbDeviceConnection, epIn: UsbEndpoint) {
-        val buf = ByteArray(512)
+        val buf = ByteArray(USB_READ_BUF_SIZE)
         while (true) {
             val len = connection.bulkTransfer(epIn, buf, buf.size, FLUSH_TIMEOUT_MS)
             if (len <= 0) break
@@ -560,7 +565,7 @@ class SettingsActivity : AppCompatActivity() {
     }
 
     private fun readResponse(connection: UsbDeviceConnection, epIn: UsbEndpoint, timeoutMs: Long): String {
-        val buf = ByteArray(512)
+        val buf = ByteArray(USB_READ_BUF_SIZE)
         val sb = StringBuilder()
         val startTime = System.currentTimeMillis()
 
@@ -613,7 +618,7 @@ class SettingsActivity : AppCompatActivity() {
 
     private fun generateRandomHexKey(): String {
         val random = SecureRandom()
-        val bytes = ByteArray(32)
+        val bytes = ByteArray(HMAC_BYTE_COUNT)
         random.nextBytes(bytes)
         return bytes.joinToString("") { "%02X".format(it) }
     }
diff --git a/android/app/src/main/java/com/eddy/atomrelay/UsbSerialTransport.kt b/android/app/src/main/java/com/eddy/atomrelay/UsbSerialTransport.kt
index 2513822..28e86e3 100644
--- a/android/app/src/main/java/com/eddy/atomrelay/UsbSerialTransport.kt
+++ b/android/app/src/main/java/com/eddy/atomrelay/UsbSerialTransport.kt
@@ -16,6 +16,7 @@ class UsbSerialTransport(
     companion object {
         private const val USB_TIMEOUT_MS = 5000
         private const val CONTROL_LINE_TIMEOUT_MS = 1000
+        private const val MIN_USB_PACKET = 64
     }
 
     override fun read(buffer: ByteArray, length: Int): Int {
@@ -42,6 +43,6 @@ class UsbSerialTransport(
     }
 
     override fun readBufferSize(): Int {
-        return epIn.maxPacketSize.coerceAtLeast(64)
+        return epIn.maxPacketSize.coerceAtLeast(MIN_USB_PACKET)
     }
 }
\ No newline at end of file
diff --git a/android/app/src/main/res/values/strings.xml b/android/app/src/main/res/values/strings.xml
index 18e103a..5176d99 100644
--- a/android/app/src/main/res/values/strings.xml
+++ b/android/app/src/main/res/values/strings.xml
@@ -86,6 +86,9 @@
     <string name="flash_chip">Chip: %s</string>
     <string name="flash_stub">Stub laden…</string>
     <string name="flash_done">Firmware geflashed!</string>
+    <string name="flash_writing">%s schrijven (%s)…</string>
+    <string name="flash_written">%s geschreven</string>
+    <string name="flash_resetting">ESP resetten…</string>
 
     <!-- Label customization -->
     <string name="section_labels">Knoptekst</string>