I just got my Fitbit flex and I think it's fantastic. If it monitors your sleep though it will have a good idea of when you're in deep (REM) sleep and when you're in lighter sleep. You cycle between these two during the night on a pretty reliable pattern, and they're easy to tell apart as you don't move around while you're in REM sleep. At least not as I understand things.
Could an update for the Fitbit modify the alarm feature please to wake you up as close as possible to your chosen time, but NOT during REM sleep?
This will allow you to wake more naturally, feeling refreshed, rather than how unpleasant it is when your alarm goes off in REM sleep.
Thanks, please all vote for this 
Moderator edit: labels.
Join us on the Community Forums!
Community Guidelines
Learn the Basics
Join the Community!
Not finding your answer on the Community Forums?
Go to the Help Site
Contact Support