Angel Sensor SDK
Angel Sensor is an open wearable for developers who're building new mobile health products. Angel Sensor tracks heart rate, skin temperature, steps, sleep quality, calories, acceleration, and orientation. It offers unrestricted, real-time API to its sensors and full control of the data. Angel Sensor SDK, Bluetooth profiles and apps are open source. The SDK supports iOS and Android.
Simply put, Angel Sensor is a wearable component to build stuff with.
Full API reference for Android can be found here.
Angel Sensor SDK is under active development. For more info, please refer to www.angelsensor.com/develop.