Ring size - 11.
ULTRAHUMAN Ring Air - Advanced Sleep-Tracking Wearable, HRV, Heart Rate & Temperature Monitoring, Track Workout, Motion & Recovery, Water Resistant to 100 m
It has been used for 6 months. The battery lasts around 2 days.
I was very pleased with the fitness tracking and the sleep stats. Its works great with the Ultrahuman app (which is free).