I really like this gadget! When I first started using it, it was weird to me how it could read my activity to measure my calories without having to use a heart rate monitor. The science behind this is the bomb!! You wear it at the top of your left arm and you don't even know you're wearin' it! You wear it while you sleep too...that way, you can see how many active hours you're sleepin'. It also tells you when you're just layin' down and finally goin' to sleep. I love it!