Transmitting over both Bluetooth and ANT+ these compact sensors capture speed, distance and pedal strokes per minute, whether you re riding outside or on a trainer. With no magnets or other exposed parts to line up, they re a cinch to install, maintain and switch between bikes. It's compatible with units that support separate channels for speed and cadence (not units that combine the 2 signals). If your device only has one menu item for speed/cadence, then this product is not compatible. Bluetooth and ANT+ secure digital transmission technology. Speed Sensor 2 has a memory allowing the unit to track your rides, even when you aren t using your phone or bike computer. The sensor will start a ride session when you start rolling and stop that session when you come to a stop, synching that ride to your phone (running Garmin Connect) or computer next time they are in range. Each unit use a single CR2032 battery life is approximately 360 hours. Range is 10m. Waterproof to 10 meters (does not function underwater).