Further thoughts on Sleeptracker

Rather than sensing sympathetic nerve activity in the skin, it's possible that Sleeptracker senses body movement instead (assuming that increased body movement is related to lighter stages of sleep).

Disclaimer: Sleep ain't my specialty. This is speculation.

Other ways of wakening: the Digital SunRise Clock by Bio-Brite wakes you with a light that slowly brightens over 20 - 30 minutes. I've used it for the last year. My review: thumbs up.