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

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 broadcastsprivate 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        }    }};

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.

In my use case I only wanted to see if a Bluetooth headset is connected for a VoIP app. The following solution worked for me.

Kotlin:

fun isBluetoothHeadsetConnected(): Boolean {    val mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter()    return (mBluetoothAdapter != null && mBluetoothAdapter.isEnabled        && mBluetoothAdapter.getProfileConnectionState(BluetoothHeadset.HEADSET) == BluetoothHeadset.STATE_CONNECTED)}

Java:

public static boolean isBluetoothHeadsetConnected() {    BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();    return mBluetoothAdapter != null && mBluetoothAdapter.isEnabled()            && mBluetoothAdapter.getProfileConnectionState(BluetoothHeadset.HEADSET) == BluetoothHeadset.STATE_CONNECTED;} 

Of course you'll need the Bluetooth permission:

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

For some reason, BluetoothAdapter.ACTION_ACL_CONNECTED could not be resolved by Android Studio. Perhaps it was deprecated in Android 4.2.2?

Here is a modification of Skylarsutton's code (Big thanks to Skylarsutton for his answer.) . The registration code is the same; the receiver code differs slightly. I use this in a service which updates a Bluetooth-connected flag that other parts of the app reference.

    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(BTReceiver, filter);    }    //The BroadcastReceiver that listens for bluetooth broadcasts    private final BroadcastReceiver BTReceiver = new BroadcastReceiver() {    @Override    public void onReceive(Context context, Intent intent) {        String action = intent.getAction();        if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)) {            //Do something if connected            Toast.makeText(getApplicationContext(), "BT Connected", Toast.LENGTH_SHORT).show();        }        else if (BluetoothDevice.ACTION_ACL_DISCONNECTED.equals(action)) {            //Do something if disconnected            Toast.makeText(getApplicationContext(), "BT Disconnected", Toast.LENGTH_SHORT).show();        }        //else if...    }};