Better measure calorie burn, understand resting heart rate & more with 24/7 heart rate tracking and a battery life of up to 7 days (varies with use and other factors). Charge time (0 100 percent): 2 hours. The operating temperature is 10 to 45 degree celsius Choose from 15 plus exercise modes like run, bike, swim, yoga, circuit training and more, set goal, and get real time stats during your workouts to see how you can keep getting better ; With aerospace grade aluminum, a smooth flush case and Corning Gorilla Glass 3, Charge 3 is comfortable and durable Automatically record time spent in Light, Deep and REM sleep stages and see activity trends, health insights and personalized guidance in one place with Fitbit Today Swim proof and water resistant to 50 Meters so you can track swims and wear in the shower (We do not recommend wearing Charge 3 in a hot tub or sauna). Also connect to smartphone GPS for real time pace and distance during outdoor runs and rides. Radio transceiver: Bluetooth 4.0 Stay connected to your day with everyday apps for weather and more and get call, text and smartphone app notifications on your wrist. Small band: Fits wrists 140 millimeter to 180 millimeter in circumference, Large band: Fits wrists 180 millimeter to 220 millimeter in circumference