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. Operating temperature: 14° to 113° F

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. Battery type: Lithium-polymer, Charge time: One to two hours, Sync stats wirelessly & automatically to computers and 200+ leading iOS, Android and Windows devices

Automatically track your steps, distance, calories burned and active minutes with up to 7 days of battery life.Changeable band

Tap to see your stats, time & notifications on an OLED display, plus customize your clock face

Operating temperature: 14 degree to 113 degree fahrenheit Maximum operating altitude: 30,000 feet

Buy with confidence when your Fitbit product 'ships from and is sold by' the following authorized Fitbit retailers:  Amazon.com, Heart Rate Monitors USA and Clever Training. Fitbit does not guarantee the quality or authenticity of products purchased from non-authorized resellers on Amazon, and they are not eligible for warranty and replacement from Fitbit

The minimum and maximum circumference range between 140 - 170 millimeters