Also, another way of stopping the alarm is flipping the device face-down for a couple of seconds.

Remember to turn it face up again asap otherwise the alarm will be dismissed, not just snoozed.

To be honest, I don't understand the behaviour completely: sometimes the alarm rings again and sometimes not.

I always try to flip the phone, wait 1 sec, then flip it face up again.. but maybe I'm too sleepy in the morning to realize the pattern.. anyone?