First of all you need to define Permission in Androindmanifest.xml 
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
<uses-permission android:name="android.permission.BLUETOOTH" />
Search Connected Devices Activity, 
private static BluetoothAdapter mBtAdapter;
private final static int REQUEST_ENABLE_BT = 1;
            // Register for broadcasts when a device is discovered
            IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
            this.registerReceiver(mReceiver, filter);
            // Register for broadcasts when discovery has finished
            filter = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
            this.registerReceiver(mReceiver, filter);
            filter = new IntentFilter( BluetoothAdapter.ACTION_DISCOVERY_STARTED );
            this.registerReceiver( mReceiver, filter );
BroadCastReceiver Class 
private final BroadcastReceiver mReceiver = new BroadcastReceiver() 
{
    @Override
    public void onReceive(Context context, Intent intent) 
    {
        try
        {
            String action = intent.getAction();
            // When discovery finds a device
            if ( BluetoothDevice.ACTION_FOUND.equals(action) ) 
            {
                // Get the BluetoothDevice object from the Intent
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
            }
        }
        catch ( Exception e )
        {
            logger.info( DateFormat.format( ConstantCodes.dateFormat ,new java.util.Date()).toString(),"Broadcast Error : " + e.toString(), ConstantCodes.SEARCH_ACTIVITY );
            System.out.println ( "Broadcast Error : " + e.toString() );
        }
    }
};