Garmin GPS Speed/ Cadence Sensor (Edge 305):
A good companion for Garmin's Edge 305 running/cycling computer, the Garmin Speed/Cadence Sensor (Edge 305) 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.
The Speed/Cadence Sensor easily to your bike, where its sensors detect signals from your wheels and send the information wirelessly to your personal trainer/cycle computer. It's also backed by a one-year warranty.