Better measure calorie burn, understand resting heart rate and more with 24/7 heart rate tracking and a battery life of up to 7 days (varies with use and other factors). Fit guide for small wrists (5.5 7.1 inches) and for large wrist (7.1 8.7 inches). Synchronizing requires bluetooth le and internet connection. Windows 10 computers that do not have bluetooth le will need a wireless sync dongle in order to synchronize. Syncs with iOS 10 and later, android 5.0 and later and windows 10 devices Choose from 15 plus exercise modes like run, bike, swim, yoga, circuit training and more, set a goal, and get real time stats during your workouts to see how you can keep getting better Automatically record time spent in light, deep and REM sleep stages, see activity trends, healthy insights, and personalized guidance in 1 place with Fitbit today. Operating temperature is -10 to 45 C Swim proof and water resistant to 50 meters, so you can track swims and wear in the shower. Also connect to Smartphone GPS in real time, pace and distance during outdoor runs and rides Stay connected to your day with everyday apps for weather and more and get called, text and smartphone app notifications on your wrist. Syncing range up to 6 meters Corning gorilla glass 3 Get a deeper understanding of your body, your health and your progress with Fitbit Charge 3. This swim proof advanced fitness tracker does more than count steps it tracks 24/7 heart rate, calorie burn, 15+ exercises, goal progress, sleep and more. Every day, you'll find valuable insights about your health that will empower you to take action, improve yourself and reach your goals.