Heart-rate tracking may not work with certain accessory bands, especially if they’re loose fitting. For best results, use the wristband that came with your device.
If you’re doing an exercise such as high-intensity interval training, boxing, or other activities that cause your arm to move vigorously, try to relax your wrist and stay still for up to 10 seconds until your heart rate appears.
Note that heart-rate tracking is disabled during swimming.
Use the Exercise app to record GPS data, including a map of your route, during a workout. If you use MobileTrack in the Fitbit app, your heart rate might not appear on your device. For more information, see How do I use GPS on my Fitbit device?