diff --git a/diaconn/src/main/java/info/nightscout/androidaps/diaconn/service/BLECommonService.kt b/diaconn/src/main/java/info/nightscout/androidaps/diaconn/service/BLECommonService.kt
index cdb8c89053..c49367ddef 100644
--- a/diaconn/src/main/java/info/nightscout/androidaps/diaconn/service/BLECommonService.kt
+++ b/diaconn/src/main/java/info/nightscout/androidaps/diaconn/service/BLECommonService.kt
@@ -167,16 +167,18 @@ class BLECommonService @Inject internal constructor(
     @Synchronized
     private fun writeCharacteristicNoResponse(characteristic: BluetoothGattCharacteristic, data: ByteArray) {
         Thread(Runnable {
-            SystemClock.sleep(WRITE_DELAY_MILLIS)
-            if (bluetoothAdapter == null || bluetoothGatt == null) {
-                aapsLogger.error("BluetoothAdapter not initialized_ERROR")
-                isConnecting = false
-                isConnected = false
-                return@Runnable
+            synchronized(this) {
+                SystemClock.sleep(WRITE_DELAY_MILLIS)
+                if (bluetoothAdapter == null || bluetoothGatt == null) {
+                    aapsLogger.error("BluetoothAdapter not initialized_ERROR")
+                    isConnecting = false
+                    isConnected = false
+                    return@Runnable
+                }
+                characteristic.value = data
+                characteristic.writeType = BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE
+                bluetoothGatt?.writeCharacteristic(characteristic)
             }
-            characteristic.value = data
-            characteristic.writeType = BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE
-            bluetoothGatt?.writeCharacteristic(characteristic)
         }).start()
         SystemClock.sleep(50)
     }
@@ -200,6 +202,7 @@ class BLECommonService @Inject internal constructor(
         return bluetoothGatt?.services
     }
 
+    @Synchronized
     private fun findCharacteristic() {
         val gattServices = getSupportedGattServices() ?: return
         var uuid: String
@@ -214,7 +217,7 @@ class BLECommonService @Inject internal constructor(
                     // nRF Connect 참고하여 추가함
                     val descriptor: BluetoothGattDescriptor = uartIndicate!!.getDescriptor(UUID.fromString(CHARACTERISTIC_CONFIG_UUID))
                     descriptor.value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE
-                    bluetoothGatt!!.writeDescriptor(descriptor)
+                    bluetoothGatt?.writeDescriptor(descriptor)
                 }
                 if (WRITE_UUID == uuid) {
                     uartWrite = gattCharacteristic