You may be interested in the S60-Application Happy Wakeup
http://www.happywakeup.com/en/How_it_works.htm

The reason why I mention it is that they use audio data from the mic rather than acceleromater sensor data (as sleeppy or the iphone apps do).

i don't know which gives the more accurate resulsts... but i just don't want to put my N900 *in* my bed. I could live with having it beside my bed or on the floor under my bed or whatever... but i wouldn't sleep well knowing each movement could throw the n900 to the floor.