Classic band (small & large). Multi-path optical heart rate sensor. Red and infrared sensors for oxygen saturation (SpO2) monitoring. Built-in GPS + GLONASS. WiFi (deactivated, cannot be turned on). Device temperature sensor (skin temperature variation available in the Fitbit app). Battery life of 6+ days. Battery life and charge cycles vary with use, settings and other factors; actual results will vary. We recommend charging your tracker every few days to ensure you are always tracking. Charge time (0-100%): Two hours. Radio transceiver: Bluetooth® 5.0. Saves 7 days of detailed motion data, minute by minute. Saves daily totals for the last 30 days. Stores heart rate data at one-second intervals during exercise tracking and at five-second intervals all other times. Water resistant to 50m. After getting the band wet, we recommend drying the band because, as with any wearable device, it’s best for your skin if the band is clean and dry. This watch includes a band made of a flexible material similar to that used in many sports watches, as well as an aluminum watch case and buckle. Learn more about wear and care tips here. Like all heart rate tracking technologies, accuracy is affected by physiology, location of device and different movements. Operating temperature: -14° to 113°F. Google account will be required. The Fitbit app is compatible with most popular phones. To set up and use your Fitbit products and services, you must install the Fitbit app on a compatible device running one of the following operating systems. Apple iOS 15 or higher. Android OS 9 or higher. See additional tips for Android phones here. Syncing range: Up to 30ft. Certain features like smartphone notifications may require Android 9+. Check your device compatibility. Print this guide to find the right size for you. Both small and large sizes included in box. Fits wrist 5.5″ – 7.1″ in circumference. Fits wrist 7.1″ – 8.7″ in circumference. 1.5in l x 1.5in w x 0.45in h.