The Oura Ring 4 is a versatile smart ring designed to monitor various aspects of health and fitness. With advanced sensors, including accelerometer, heart rate, PPG sensor, and temperature, it provides comprehensive tracking of sleep activity, heart rate, blood oxygen saturation ...The Oura Ring 4 is a versatile smart ring designed to monitor various aspects of health and fitness. With advanced sensors, including accelerometer, heart rate, PPG sensor, and temperature, it provides comprehensive tracking of sleep activity, heart rate, blood oxygen saturation, and menstrual cycle data.