Disclaimer: Sleep isn't my specialty. My experience may not be yours.
I've evaluated Sleeptracker for one week, and I can't detect any significant difference in my sleep or wakening. To recap: Sleeptracker is a watch which is designed to detect REM or stage 1 sleep and wake you up at the "optimal" time.
This sounds good in theory, but in order for this to be effective the following must be true:
- REM or stage 1 sleep must be sensed,
- the stages of sleep must be sensed accurately,
- there must be a noticeable benefit to wakening in the lighter stages of sleep.
The problem is this: the Sleeptracker website doesn't say how it works. This is understandable, but it means there is no way to verify that #1 or #2 is true. Number 3 intuitively seems true, but no evidence is cited to back this up.
Personally, I have not noticed that I wake easily or feel unusually refreshed when using Sleeptracker. There could be many reasons for this (and again, my experience may not be yours), but for a product this expensive, I would hope for a more obvious benefit.