The Polar G3 GPS Sensor is a lightweight GPS device which, with the RS800, provides speed & distance measurement in all terrestrial sports such as running, rowing, mountain biking & canoeing. The sensitive SIRF III GPS system provides highly reliable GPS reception even in wooded areas. Up to 15 hours power consumption (up to 30 hours with optional lithium battery). Only 80g including battery. Uses one, easy to replace AA battery. Water resistant to 3 bar. Compatible with the Polar RS800, RS800sd & RS800G3.