The problem is, not only it's inaccuracy, as many others have mentioned in the reviews, but also the unfriendly was of its menu (I am not capable to start the sleep monitoring function! You click on it and nothing happens!!) The battery sucks
But what makes this product useless after not even 4 times I've used to go for a run of 30 minutes, and one night attempt of sleep monitoring, is the fact that it doesn't charge anymore!!
You plug it in onto the USB socket and it simply doesn't charge
Waste of money, should have invested more for a more serious product