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.