Never opened, brand new Fitbit Sense! 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. 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. 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. 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. 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. 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.