To get the signal you can check Bluetooth RSSI, you can read RSSI for connected devices, or perform a Bluetooth discovery to check the RSSI for any nearby devices.
Basically a Bluetooth discovery is a broadcast to all stations within range to respond back. As each devices responds back, Android fires off an ACTION_FOUND intent. Within this intent you can getExtra EXTRA_RSSI to obtain the RSSI.
Note that not all bluetooth hardware supports RSSI.
Also Related: Android IRC Office Hours Question About Android Bluetooth RSSI
here is a Bluetooth Classic broadcast receiver example
private final BroadcastReceiver receiver = new BroadcastReceiver(){
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if(BluetoothDevice.ACTION_FOUND.equals(action)) {
short rssi = intent.getShortExtra(BluetoothDevice.EXTRA_RSSI,Short.MIN_VALUE);
Toast.makeText(getApplicationContext()," RSSI: " + rssi + "dBm", Toast.LENGTH_SHORT).show();
}
}
};