NEW Irregular heart rhythm notifications This feature analyzes your heart rhythm during sleep or while at rest to let you know if it shows signs of Atrial fibrillation. #AFib is an irregular heart rhythm that can show up, well, irregularly & can be hard to detect during doctor visits. See our link in bio to set this feature up. *** Available in select countries; not intended for use by people under 22 years old or with known atrial fibrillation. See fitbit.com/irregularrhythm for additional details.