如果您希望在应用关闭时触发闹钟，可以考虑使用Service来保持应用运行。您可以在Service中使用AlarmManager来触发您的闹钟。以下是一个示例代码：

public class AlarmService extends Service {

private static final int INTERVAL = 20 * 1000; // 20 seconds
private static final int FIRST_RUN = 5000; // 5 seconds
private static final String TAG = "AlarmService";

private Context context;
private Handler handler = new Handler();

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    context = this;

    // set up the alarm
    AlarmManager manager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
    Intent alarmIntent = new Intent(context, AlarmReceiver.class);
    PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, alarmIntent, 0);
    manager.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + FIRST_RUN, INTERVAL, pendingIntent);
    Log.d(TAG, "Alarm set.");

    // create a thread to keep the service running
    Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
            while (true) {
                try {
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    });
    thread.start();

    return START_STICKY;
}

@Override
public IBinder onBind(Intent intent) {
    return null;
}

}

在Service中，我们首先设置了间隔和第一次运行时间，并使用AlarmManager重复触发我们的闹钟。然后，我们创建一个线程来保持Service运行，以确保我们的闹钟可以在应用关闭时保持运行。

我们还需要创建一个广播接收器来接收闹钟的触发事件，如下所示：

public class AlarmReceiver extends BroadcastReceiver {

private static final String TAG = "AlarmReceiver";

@Override
public void onReceive(Context context, Intent intent) {
    Log.d(TAG