Any alarm clocks for PC?

How do "sleep cycle" alarm clocks work, and are they effective?

• I have heard about "seep cycle" alarm clocks, such as the one for iPhone (http://www.sleepcycle.com/) which uses the device's accelerometer to keep track of how you move when you sleep. How do alarm clocks such as this work on a scientific level? Is there any proof one way or another, besides anecdotal evidence, that they do anything at all to help people wake up in the morning and be more rested?

• Answer:

  I actually wrote the sleep state detection algorithm for a sleep cycle alarm clock iPhone app called Proactive Sleep(http://proactivesleep.com/), so I can give a general sense of what we used. We based the algorithm off a research paper that discussed how to detect sleep and awake states (called Actigraphy I think). We'd take the acceleration from the iPhone's accelerometer every 100 or so milliseconds, filter out small vibrations, and count the number of times the acceleration changed from negative to positive for each minute. We'd store this data for the previous 7 or so minutes, and then there was an equation we plugged the counts into which weighted each minute's counts differently. If the resulting number was above a certain threshold, we called it awake, and vice versa for asleep. By constantly doing this each minute, we could detect whether the person was asleep or awake. That's just how we did it though.