Classic band (small & large). Multi-path optical heart rate sensor. Electrical sensor to measure skin conductance (cEDA) for body response tracking. Multipurpose electrical sensors compatible with ECG app & EDA app. ECG not available in all countries. Red and infrared sensors for oxygen saturation (SpO2) monitoring. WiFi (deactivated, cannot be turned on). Built-in GPS + GLONASS. Battery life of 6+ days. Battery life and charge cycles vary with use, settings and other factors; actual results will vary. Use of the always-on display, SpO2 and the cEDA sensor will require more frequent charging. Up to 5 hours with continuous GPS. We recommend charging your tracker every few days to ensure you are always tracking. Charge time (0-100%): Two hours. Charge 12 minutes to get one day of battery life. 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. Give your wrist a rest by taking the band off every now and then. If the band gets wet or you sweat in it, remove and completely dry the band before putting it back on. 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. 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. Small: Fits wrist 5.5″ – 7.1″ in circumference. Large: Fits wrist 7.1″ – 8.7″ in circumference. 1.5″ l x 1.5″ w x 0.45 h.