How to update database after every 24 hour in Android

In my application I'm using a button to update my sqlite database but now I want to update my database automatically after every 24 hours. How can I do this? I tried using CountDownTimer but that does not work when my app isn't running. I tried pending Intent and Alarm Manager but it isn't working properly(P.S: I tested it for 10 seconds instead of 24 hrs). It works for the 1st time when I start my activity and then it stops and doesn't work. Here's the code I tried:

public class Activity_Settings extends ActionBarActivity{
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
 Intent notificationIntent = new Intent(mActivity, MyAlarmService.class);
        PendingIntent contentIntent = PendingIntent.getService(mActivity, 0,   
 notificationIntent,0);

        AlarmManager am = (AlarmManager) 
          getSystemService(Context.ALARM_SERVICE);
        am.cancel(contentIntent);
        am.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis()
                + AlarmManager.INTERVAL_DAY * 1, AlarmManager.INTERVAL_DAY * 
        1, contentIntent); 

  }
  }

Service class:

 public class MyAlarmService extends Service {



@Override

public void onCreate() {

// TODO Auto-generated method stub
      Intent mainIntent = new Intent(this,Activity_Settings.class);
Toast.makeText(this, "MyAlarmService.onCreate()", Toast.LENGTH_LONG).show();

// update database
}



@Override

public IBinder onBind(Intent intent) {

// TODO Auto-generated method stub

Toast.makeText(this, "MyAlarmService.onBind()", Toast.LENGTH_LONG).show();

return null;

}



@Override

public void onDestroy() {

// TODO Auto-generated method stub

super.onDestroy();

Toast.makeText(this, "MyAlarmService.onDestroy()", Toast.LENGTH_LONG).show();

}



@Override

public void onStart(Intent intent, int startId) {

// TODO Auto-generated method stub

super.onStart(intent, startId);

Toast.makeText(this, "MyAlarmService.onStart()", Toast.LENGTH_LONG).show();

}



@Override

public boolean onUnbind(Intent intent) {

// TODO Auto-generated method stub

Toast.makeText(this, "MyAlarmService.onUnbind()", Toast.LENGTH_LONG).show();

return super.onUnbind(intent);

}



}