A wireless sensor measuring cycling speed and distance via a magnet rotating on the front or the rear wheel depending on the sensor. Includes bike mount. The Speed Sensor is included in the Polar S-510, S-520 and S-710i, S-720i heart rate monitor sets and is purchased separately to fit to another bicycle. Compatible with the Polar S-510, S-520 and S-710i, S-720i heart rate monitors.