EDA Scan app detects electrodermal activity which may indicate your body's response to stress and a built-in skin temperature sensor logs yours each night so you can see when it varies.Band Size : Small : Fits wrist 140mm - 180mm in circumference. Large : Fits wrist 180mm - 220mm in circumference Assess your heart for atrial fibrillation ?a heart rhythm irregularity- and easily share results with your doctor (The Fitbit ECG app is only available in select countries. Not intended for use by people under 22 years old.Operating temperature: 14 to 113F An on-wrist skin temperature sensor tracks yours each night so you can see how it varies. You can also see your nightly blood oxygen levels at a glance with our collection of clock faces.Radio transceiver: Bluetooth 5.0.Operating temperature: -10 to 45 C High low heart rate notifications alert you if yours seems above or below your average.Battery lasts 6 plus days plus, fast charging gives you a full day's charge in just 12 minutes (Varies with use and other factors; up to 12 hours with continuous GPS).Use built-in GPS during runs, hikes, rides and more to see pace distance without your phone and use the built-in mic and speaker to take Bluetooth calls hands-free when your phone is nearby (Requires more frequent charging). Meet Fitbit Sense?the advanced smartwatch that helps you tune in to your body and guides you toward better health. Assess your heart for atrial fibrillation (Afib) with a compatible ECG app right on your wrist, track manage stress, better understand your sleep quality and even keep an eye on patterns in your skin temperature. Plus, Sense unlocks a 6-month free trial of personalized guidance and advanced insights from Fitbit Premium for new users. Fitbit is part of the Google family. Requires use of Fitbit app with compatible iPhone or Android devices. A Google account will be required.