Alarm Clock : Calm & Timer

I wanted a clock app that had a timer, so I'd be waked up after a, say, 40 min. nap. Apple's clock isn't reliable in that if often makes no sound when the time ends. This clock has yet to make _any_ sound when the timer runs out of time. Worse, the timer loses time; last week I set an alarm for a physician appointment, but that was a day the clock was 57 mins behind. That cost me $45 for the missed appointment.