Polar 91047327 Speed and Cadence Sensor Bluetooth Smart Set Improves your cycling technique and performance Speed sensor accurately measures your cycling speed and distance. Cadence sensor measures the real-time and average pedaling rate of your ride. Small and light design with firm bike attachment. Uses Bluetooth low energy wireless technology. Compatible with Polar V800 , Polar V650, popular cycling apps, the iPhone 4S and later and select Android devices using Android 4.3 or later Set includes one Polar Bluetooth Smart speed sensor and one Polar Bluetooth Smart cadence sensor