Check the listing for details. Oura Ring 4 Ceramic Midnight Bluetooth Activity Tracker Size 11 Brand New sealed. Color: Midnight, Condition: New, Made in United States. Listed at 299.00 USD. The Oura Ring 4 Ceramic Midnight Bluetooth Activity Tracker in size 11 is a high-tech tool designed for fitness enthusiasts, particularly those involved in running and jogging. With a sleek ceramic design in a midnight color, this activity tracker is equipped with Bluetooth connectivity for seamless data transmission. Its compact size allows it to be worn comfortably on the finger, making it an ideal companion for tracking and monitoring your fitness progress. The ring comes sealed, ensuring its authenticity and quality. Compatible with both iOS and Android operating systems, this activity tracker offers a range of features to help you stay on top of your fitness goals.