This is the Sigma BC 2006 cyclometer. The wheel sensor is wireless. The main unit, the wheel sensor, and the heart monitor strap each use a CR2032 battery. The power in the main unit shuts down automatically when not in use, but the wheel sensor broadcasts a digital signal 24 hours a day, 7 days a week. Battery life in the wheel sensor is disappointingly short. The batteries are relatively expensive. I wanted a way to control the battery drain from the sensor and provide a less expensive source of power.