Disclosed herein is a ring-shaped wearable device for detecting biometrics with a light source and a photodetector directed towards a digit wearing the ring-shaped device. The ring can thus detect oxygen saturation of a wearer based on light transmitted through the wearer's finger. The ring can include power saving measures to extend the battery life. A motion sensor can help determine opportune moments for data collection such as when the wearer is still. The motion sensor can be used to remove noise from the data caused by motion. After data is collected or during data collection, the ring can wirelessly communicate the data to another portable electronic device such as a phone or watch.