Angel is a sensor that comes with a slick shaped wearable device and several useful data streams, such as optical PPG (heart rate), 3D accelerometer, 3D gyroscope and temperature. They even plan a blood oxygen sensor for a future device update.
Their API grants access to real-time raw data to be able to process it on the fly. For wireless data transport they chose Bluetooth LE. Needless to say it would be a great improvement to make use of it in our final implementation. Unfortunately it is out of stock this minute. Maybe we will have a chance to get one with the next batch.