title: Detect nearby presence of Android Device via Bluetooth
body: <p>Is there any smart way for an App installed on 2 devices close to each other to recognize themselves via Bluetooth without asking anything to the user ? 
  Note that I'm not talking about transferring data or any other operation, I just want to know (for sure) that this particular device is close to me (for example a simple shared ID or hardware address would be far enough).</p>
  
  <p><strong>Important :</strong> it has to work from Android 4.4 to Android 6, so it means that : </p>
  
  <ol>
  <li>We cannot rely on BluetoothLeAdvertiser because it's only from API 21. </li>
  <li>We cannot rely on BluetoothAdapter Mac Address recognition because <a href="https://developer.android.com/about/versions/marshmallow/android-6.0-changes.html#behavior-hardware-id" rel="nofollow">it is now broken and randomized</a> from API 23. </li>
  </ol>