The Oura Ring 4 Ceramic in Midnight, Size 15 is a discreet smart ring with Smart Sensing — tracking 50+ signals across sleep, readiness, heart, stress, and metabolic health. Up to 8 days of battery, no screens, no buzz. Daily Readiness Score from sleep, HRV, blood oxygen, and temperature trends Pairs with the Oura app on iOS or Android. First month of membership included; $7.99/mo after This description was generated by AI and reviewed for accuracy.