Please refrain from purchasing if you are concerned, as this item is used. Size US8 Red light and infrared LEDs measure blood oxygen wellness. Green light and infrared LEDs alternately measure heart rate and heart rate variability 24/7, and measure respiration rate. Digital sensors measure changes in body surface temperature trends. An accelerometer tracks activity and body movement 24/7. Oura App supported languages: Czech, Danish, Dutch, English, Finnish, French, German, Italian, Japanese, Norwegian, Spanish, Swedish Supports metric and imperial units. Works with over 40 apps. Available on iOS and Android. Width: 7.90mm Thickness: 2.88mm (similar to a wedding ring) Weight: 3.3-5.2 grams (varies depending on Oura Ring size) Charging complete in 20-80 minutes (depending on battery level) Non-allergenic titanium is used on the inner and outer surfaces of the ring. The inside of the ring is smoothly molded using titanium. Water resistant up to 100m. Small scratches may occur over time with normal use. Connectivity Bluetooth Low Energy (Bluetooth Smart®) Automatic firmware updates via the Oura App EMF (low-frequency magnetic field) conscious design Airplane mode compatible FCC certified