Garmin GSC 10 Speed/Cadence Bike Sensor for $37.99

A good companion for Garmin's Edge 305 and 305CAD cycle computers and the Garmin Forerunner 305 personal trainer, the GSC 10 monitors your cycling rhythm for up-to-the-minute results and later analysis. The self-calibrating, wireless unit measures both speed (in pedaling strokes per minute) and cadence , then provides feedback to the user for optimal performance. You can later feed the results to Garmin's Training Center software, which helps you tailor your workouts to meet specific goals and objectives.