About this item: 
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 113°F 
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. Maximum operating altitude: 28,000ft 
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) 
Use Google Assistant or Amazon Alexa Built-in to get quick news, set bedtime reminders and alarms, control your smart home devices, and more just by speaking to your watch