Wahoo's ANT+ Speed/Cadence Sensor pairs with your iPhone to display your speed and cadence.
• Requires an ANT+ receiver such as a Wahoo Key or Bike Case and iPhone for use (each sold separately)
• Mounts on rear chain stay and uses spoke and crank magnets to track instantaneous bike speed and pedal rotations per minute
• Water and shock proof: IPX7 Certified
• Long-lasting, replaceable coin cell battery; no need for extra cables or recharging
• Weight: 30 grams