How can I programmatically tell if a Bluetooth device is connected?

Question

I understand how to get a list of paired devices, but how can I tell if they are connected?

It must be possible since I see them listed in my phone's Bluetooth device list and it states their connection status.

Answer 1

Add the Bluetooth permission to your AndroidManifest,

<uses-permission android:name="android.permission.BLUETOOTH" /> 

Then use intent filters to listen to the ACTION_ACL_CONNECTED, ACTION_ACL_DISCONNECT_REQUESTED, and ACTION_ACL_DISCONNECTED broadcasts:

public void onCreate() {     ...     IntentFilter filter = new IntentFilter();     filter.addAction(BluetoothDevice.ACTION_ACL_CONNECTED);     filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECT_REQUESTED);     filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECTED);     this.registerReceiver(mReceiver, filter); }  //The BroadcastReceiver that listens for bluetooth broadcasts private final BroadcastReceiver mReceiver = new BroadcastReceiver() {     @Override     public void onReceive(Context context, Intent intent) {         String action = intent.getAction();         BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);          if (BluetoothDevice.ACTION_FOUND.equals(action)) {            ... //Device found         }         else if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)) {            ... //Device is now connected         }         else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {            ... //Done searching         }         else if (BluetoothDevice.ACTION_ACL_DISCONNECT_REQUESTED.equals(action)) {            ... //Device is about to disconnect         }         else if (BluetoothDevice.ACTION_ACL_DISCONNECTED.equals(action)) {            ... //Device has disconnected         }     } }; 

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A few notes:

• There is no way to retrieve a list of connected devices at application startup. The Bluetooth API does not allow you to query, instead it allows you to listen to changes.
• A hoaky workaround to the above problem would be to retrieve the list of all known/paired devices... then trying to connect to each one (to determine if you're connected).
• Alternatively, you could have a background service watch the Bluetooth API and write the device states to disk for your application to use at a later date.