The Mio Alpha 2 has Bluetooth Smart 4.0 technology, allowing you to connect with your smartphone (Android or iOS). It sends your data of heart rate to your apps on the smartphone. This watch is multifunctional. You can use it not only for stress monitoring but also for your physical work out programmes (it has 2-way communication), or you can just wear it as a digital watch. It has a rechargeable Li-ion battery. Battery life in workout mode is approx. 20hrs.