Occasionally your device may have difficulty getting a strong signal, especially during exercises that cause your arm to move vigorously such as high-intensity interval training or boxing. Try to relax your wrist and stay still for up to 10 seconds. You might also notice a spike or dip in your reading as your device finds your heart rate. In both cases, normal tracking should resume shortly.
See more tips in How do I track heart rate with my Fitbit device?
Your watch is searching for a stronger reading, and normal tracking should resume shortly.
Heart-rate tracking is turned on automatically. If you turned heart-rate tracking off, turn it back on:
On your device, open the Settings app 
On Fitbit Alta HR and Fitbit Charge 2, you must turn on heart-rate tracking in the Fitbit app:
- Tap the Today tab
, and tap Devices
.
- Tap your device image.
- Tap Fitbit reminders & alerts
Note that you can’t turn off heart-rate tracking on Fitbit Sense, Fitbit Sense 2, Fitbit Versa 3, or Fitbit Versa 4.
- Tighten the band so that it doesn’t slip on your wrist. For more information, see How do I track heart rate with my Fitbit device?
- Heart-rate tracking may not work with certain accessory bands, especially if they’re loose fitting. For best results, use the band that came with your device.
- Use the Exercise app
to record GPS data for your 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?
- If you tried the other steps and don’t see your heart rate, restart your device. For more information, see How do I restart my Fitbit device?