This works fine:

Intent intent = new Intent(HelloAndroid2.this, AlarmReceiver.class);

    PendingIntent pendingIntent = PendingIntent.getBroadcast(HelloAndroid2.this, 0,
    intent, PendingIntent.FLAG_ONE_SHOT);

    AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
    alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + (12 * 1000), pendingIntent);

This doesn't work. I hear the alarm only time.

alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + (12 * 1000), 3 * 1000, pendingIntent);

I have also tried this, no luck:

Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(System.currentTimeMillis());
    calendar.add(Calendar.SECOND, 5);

    alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), 7000, pendingIntent);

What is the problem?