Topeak panobike bluetooth smart cadence & speed sensor

With Bluetooth® Smart super low energy technology. Works with iPhone 4S/5 and iPod Touch with BLE 4.0. Advanced Bluetooth® Smart (BLE 4.0) super low energy consumption wireless speed & cadence dual sensor provides real-time ride information on your mobile training Apps and turns your smartphone into a personal training device. Unique Bluetooth® Smart algorithm extends battery lifetime up to incredible 1800 hours (5 years with 1hr/day use) - 21 g