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• Get the power of continuous heart rate in Fitbit's slimmest design yet-all day, during workouts and beyond
• With heart rate, you can better measure calorie burn, and use zones (Fat Burn, Cardio, and Peak) to find the right workout intensity for your goals.Fits wrists 5.5in - 6.7in in circumference
• With sleep stages powered by PurePulse heart rate, automatically track your time spent in light, deep and REM sleep and take steps toward a better night's rest.
• See how working out more can improve your health by comparing your resting heart rate trends to your activity, Sync stats wirelessly & automatically to computers and 200+ leading iOS, Android and Windows devices.