The alarm is part of the mobile app and it works in a similar way to the stock alarm clock app only informed by your current sleep phase.

Here's the difference.

Say you set your alarm for 7 am. The app starts looking at the sleep phase you are in from 6:30 am (this is configurable), if you enter a light sleep phase (N1) at 6:45, the alarm goes off and wake up without feeling groggy. If you don't enter a light sleep phase, the alarm goes off regardless at 7 am so you don't miss meetings and such.