This is the Polar G5 GPS sensor which provides accurate distance and speed measurement for a wide range of outdoor sports. It has been designed to be light and easy to wear and have a GPS clip. After you have completed training you will be able to see your route on a map with compatible software/web service. At 34g they are ultra light and are small at 39 x 64 x 12 mm. They measure speed, pace and distance and also record accurate GPS positioning. The G5 GPS sensor is powered by a rechargeable battery via a micro USB and has a 20 hour life.