Zacro Bluetooth-Enabled Wireless Electron Heart Rate Monitor, with an Original Battery Replacement, Waterproof up to 5 Feet, Compatible with iPhone Models, IPad and Android Smartphones. The most accurate heart rate due to ECG-based technology; With soft belt strap, it will provide live heart rate to compatible mobile training apps For optimal battery life, detach transmitter from chest strap after every use; Besides, we also offer an Zacro orginal replacement battery for free Compatible devices: Apple iPhone 4S (and later) Apple iPad 3 (and later) and smartphone with Android 4.3 (and later) with Bluetooth 4.0 Portable and wearable when running or doing other athletic sports Low power consumption and durable service; Therefore, it has more than one year battery life