ive read up on it because i have been interested in it as well. from what i have learned, many seem to not think it is very accurate only it is based on movement, like a kinetic watch where it stays powered with every movement you make with your hand/wrist. So whenever they keep it on whenever they are inactive, any hand movements log as activity and counts calories. However, i would actually only use it whenever i am doing something (i.e. working out/ playing baseball) so i can get some sort of idea what i am doing. i wouldnt keep it on and keep wearing it whenever im asleep. so i am sort of still leaning towards getting one. hope this helps some.