I have read the bad reviews for this product, yet decided this because compared products not much get better reviews. Of course, the product may not work well. The main problem, however, I believe that the manual a 'Plug and Play solution' suggested. However, this is not enough. You have to actually read what it says in the manual and in the runtastic app also select the correct product when ordering. Not choose the chest 'Combo' from, it also does not work with the Bluetooth connection. Also you will notice upon closer inspection of the belt that you have to pull it NOT over his head, was as detailed in other reviews. My belt has at least one hook where I can make the belt and on again. So: On my 4S I had the belt after 5 minutes functional, so 5 stars. But perhaps I had just luck.