I use gsAlarmClock myself - 100% reliable. You do NOT need to launch it, or leave it running, for an alarm to go off if its set. Heck, you can even soft-reset after setting an alarm.The app uses the notification queue (correctly

) to schedule the alarm.
Just make sure you close the app once you check the alarm checkbox by tapping the x box.
I've never missed an alarm with this app.