There are lots of tricks we can use to make our alarms less horrific, but, ideally, we shouldn't need shrieking or even pleasant alarm clocks at all to wake up on time, bright and refreshed. Mental Floss explains why.
If you're one of the elite who regularly wake up five minutes (or so) before the alarm, here's the science behind it:
Your body hates your alarm clock. It's jarring. It's stressful. And it ruins all that hard work. It defeats the purpose of gradually waking up. So, to avoid being interrupted, your body does something amazing: It starts increasing PER [the protein that regulates our sleep-wake cycle] and stress hormones earlier in the night. Your body gets a head start so the waking process isn't cut short. It's so precise that your eyelids open minutes—maybe even seconds—before the alarm goes off.
If you're not waking up before your alarm clock, the article says, you're probably not getting enough sleep. (It could also be a sign that you need to have a more regular, predictable sleep routine.)
You can mentally train yourself to wake up on time too; researchers have found that our stress hormones adjust at night to the time we think we're going to wake up.