I have never understood this 'sleep tracking' gimmick. When I wake up I know how well I slept or didn't sleep. I can't see myself checking a graph on my watch after waking up feeling like crap and going "oh my watch says I slept fine. I must be wrong." or vise versa. It's about as useful as weather reports on the evening news that tell me what the weather was for the day - I know what the weather was, I was there.