Smart Ring Heart Rate Blood Oxygen Sleep HRV Heart Rate Variability Stress Test Intelligent Finger Ring ManufacturerColor: Black ,Silver ,Gold Battery Capacity: 16mAh Appearance Size: Size 7, Size 8, Size 9, Size 10, Size 11, Size 12, Size 13 Product Weight: 3. 2g Applicable Population: Elderly, Teenagers, Men, Women Wearing Method: Ring Applicable System: iOS, Android After sales Service: Store Three Guarantees Packaging List: Ring, Manual, Charger, Packaging Box Model Inner Diameter Circumference Size 7 17. 4mm 54. 6mm Size 8 18. 2mm 57. 1mm Size 9 19mm 59. 6mm