Wahoo RPM Cadence Sensor.

The Wahoo RPM cadence sensor is your sleek little solution for measuring cycling cadence data. It is wireless, magnet-less, lightweight, and easily mounts to your bike's crank arm or to your shoe. Bluetooth Smart and ANT+ dual band technology allows you to connect to and display data on both smartphones and GPS bike computers. Collecting cadence data has never been this easy.

Specs:

• Part Number: WFPODCAD2
• Physical Dimensions (LxWxH): 1.25" x.75" x 1"
• Weight: 7 grams
• Battery: CR2032
• Battery Life: Up to 12 months
• Water Rating: IPX7 (waterproof up to 5 ft)
• Wireless Signal Strength Up to 10 feet