I've been evaluating Sleeptracker, which is a digital wristwatch that is designed to sense when you are "almost awake" (at the lightest stage of sleep) and wake you at that time. I am interested in papers or resources that could answer the following questions:
1. How does Sleeptracker sense the stages of sleep?
2. How accurate is it at determining sleep stages?
3. What evidence exists that awakening during the lightest stage of sleep is beneficial?