It says your heart rate is… just 80 bpm? And check out our guide to the best smart rings to see if they're a better option. Heart rate accuracy on smartwatchesWe judge these trackers by looking at the error rate. A sudden rise in your resting heart rate can be the first sign you are getting sick or stressed. It had the second best Resting Heart Rate accuracy (1.03%), just behind Polar (0.88%).