Zacro Wireless Heart Rate Monitor for iPhone Models, iPad and Android Smartphones BT4.0 wirelessly conveniently delivers your real-time heart rate to your fitness APP of compatible device instantly; instantlydelivers your real-time heart rate User replaceable battery, For optimal battery life, detach transmitter from chest strap after every use; Besides, we also offer an Zacro original replacement battery Waterproof Silica Gel Electrode could have a good contact with your skin and is more sensitive to transmit the heart rate 25"-42" Adjustable soft elastic fabric chest strap is also waterproof and has a comfortable completely secure fit Compatible devices: Apple iPhone 4S (and later) Apple iPad 3 (and later) and smartphone with Android 4.3 (and later) with Bluetooth 4.0