I bought this cardio POLAR belt connected to my watch POLAR M400, thereby automatically synchronizing and fast, no manipulation to just plug in lluetooth his phone, and the phone is otherwise the synchronization cardio transmitter is compatible with my samsung note 3 android 4.4.2 without any problems. The belt is comfortable to wear it is not used too much and does not make red marks on the skin. Now for the battery life we'll see how long it lasts. I suggest that H7 POLAR belt for all people who want a cardio POLAR transmitter for their shows or other applications. Fast shipping and neat as usual, thank amazon.