[brianpan]

When I was young, I would prepare to wake up before the alarm if I really wanted to make sure I didn't oversleep. I would stare at the current time for about a minute and then go to sleep. The next day I would always wake up a few minutes before the alarm.

I don't think it's magic. There are plenty of cues (sound and light) that can tell you approximately what time it is without being conscious.