How accurate are these sleep tracker devices?

[yalag]

I'm looking into buying a wearable device (something like the Jawbone UP or Fibit flex) that allows me to track my sleep. I'm interested in getting as accurate data as possible as I don't have good sleep. Does anyone know how good these devices are at tracking and which brand has it best?

 

[darster]

Not very good. They base it on movement, which is not very good at telling you how good a sleep you had. You need something to track your REM sleep, etc, which can only be done by tracking your brain waves.