要接收已连接的低功耗蓝牙设备的广播，可以按照以下步骤进行操作：

1. 创建一个广播接收器类，用于接收低功耗蓝牙设备的连接状态变化广播。可以按照以下代码示例创建一个名为BluetoothBroadcastReceiver的类：

public class BluetoothBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();

        if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)) {
            // 设备已连接
            BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
            // 处理已连接设备的逻辑
        } else if (BluetoothDevice.ACTION_ACL_DISCONNECTED.equals(action)) {
            // 设备已断开连接
            BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
            // 处理已断开连接设备的逻辑
        }
    }
}

2. 在你的Activity或Service中注册广播接收器。在适当的位置（例如onCreate方法）中添加以下代码：

private BluetoothBroadcastReceiver mBluetoothReceiver;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // 创建并注册广播接收器
    mBluetoothReceiver = new BluetoothBroadcastReceiver();
    IntentFilter filter = new IntentFilter();
    filter.addAction(BluetoothDevice.ACTION_ACL_CONNECTED);
    filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECTED);
    registerReceiver(mBluetoothReceiver, filter);
}

@Override
protected void onDestroy() {
    super.onDestroy();

    // 取消注册广播接收器
    unregisterReceiver(mBluetoothReceiver);
}

这样，当低功耗蓝牙设备连接状态发生变化时，广播接收器将接收到相应的广播，并执行相应的逻辑。你可以根据需要在广播接收器的onReceive方法中处理已连接或已断开连接设备的逻辑。