How do these "smart" alarm apps that supposedly track

File: 134996-134866.png (70KB, 300x450px) Image search: [Google]

70KB, 300x450px

How do these "smart" alarm apps that supposedly track your sleep and wake you up gently actually wake you up? Do they just sound the alarm or do they also do more subtle stuff like light vibration a few minutes before your set time to get you out of deep sleep without you noticing?

I tried sleep cycle two nights in a row and both times woke up in the set time, right before the alarm started and without me noticing anything, feeling like I normally would waking up naturally, but I can't tell if it's just coincidence or if the app actually did something right.