Google's heart rate article says a blank, frozen or gray reading usually means the device is searching for a stronger signal: relax your wrist and stay still for up to 10 seconds, especially after vigorous arm movement in interval training or boxing, and normal tracking resumes. Heart-rate tracking is on by default; if you turned it off, turn it on in the device's Heart Rate setting, though you cannot turn it off on the Sense 2 or Versa 4.
Wear the device on top of the wrist, with the back touching your skin, about a finger's width above the wrist bone at rest and a bit tighter and higher during exercise; a tight band restricts blood flow and a loose accessory band may not track. Cold weather affects blood flow. Use the Exercise app so GPS and heart rate record together, since MobileTrack in the app may hide the reading on the device. Google also lists air temperature, stress, caffeine, alcohol, illness and medication as things that change heart rate.
Differential
Likely causes of “Fitbit trackers and smartwatches heart-rate readings are missing or inaccurate”, and how to tell them apart
- 1
A loose or slipping band
What separates it Readings drop out during exercise because of a loose or slipping band
How to confirm Tighten and wear the device higher on the wrist during exercise
- 2
Vigorous arm movement
What separates it The reading is blank during boxing or HIIT because of vigorous arm movement
How to confirm Relax your wrist and stay still for up to 10 seconds
- 3
Heart-rate tracking is off
What separates it There is no reading at all because heart rate tracking is off
How to confirm Turn it on in the device's Heart Rate setting
- 4
Cold weather
What separates it Readings fail outdoors because of the cold weather on the wrist
How to confirm Warm the wrist, and try the reading again
- 5
An accessory band
What separates it Tracking fails with a loose third party band because of an accessory band
How to confirm Use the band that came with the device
Before you touch a setting
Record this first — changing settings destroys the evidence
- The model, firmware version and band
- Which reading fails and during what activity
- Which wrist and how tight the band is
- Whether tracking is turned on and whether MobileTrack was used
Try in this order
0 of 7 completedCheck tracking is on
ReversibleCheck tracking is on, by opening the device's Heart Rate setting and looking at its state.
Fix the fit
ReversibleFix the fit, by wearing it on top of the wrist with the back touching your skin.
Tighten for exercise
ReversibleTighten for exercise, by wearing it a bit tighter and higher up the wrist for workouts.
Hold still
ReversibleRelax the wrist and stay still for up to 10 seconds if the reading is blank.
Use the Exercise app
ReversibleUse the Exercise app, and record workouts with the device rather than MobileTrack, and then test again to see whether it helped.
Use the original band
ReversibleUse the original band, since loose accessory bands can stop tracking from working, and then test again to see whether it helped.
Restart
ReversibleRestart the device, and re check the reading once it comes back on, and then test again to see whether it helped.
Model-specific
What is true of this model and not of its siblings
- Tracking by model
- Google says heart-rate tracking is on by default and cannot be turned off on the Sense 2 or Versa 4; on the Charge 5, Charge 6, Inspire 3 and Luxe you can turn it on or off in the device's Heart Rate setting.
- Ace LTE
- Google's specifications list an optical heart rate sensor on the Ace LTE.
- Repair cost
- Fit and settings cost nothing. A dead sensor is a hardware fault; Alibaba's guide puts a mail-in service at $45 to $75 and a Charge 6 replacement at $99 to $129.
- Other models this page answers
- These steps also fit models Charge 5, Sense 2, Versa 4, Inspire 3, Luxe, Ace LTE.
Stop boundary
When this stops being a self-service repair
- !If the sensor lens is cracked or readings are absurd on both wrists, contact Fitbit support
- !If you have symptoms such as chest pain or dizziness, contact a doctor rather than relying on the tracker
- !If a chest strap agrees, fit is the fix
Evidence ledger
Sources behind this answer
Blank or gray readings, turning tracking on and the tips list.
Fit, position and how tracking works.
Accuracy and limitations.
High and low heart-rate alerts and vibration checks.
The Fitbit brand and its devices.
Exact questions
Common questions
Why is my heart rate gray?+
Google says the watch is searching for a stronger reading and normal tracking should resume shortly.
Why is it blank?+
Vigorous arm movement can make it hard to get a signal; relax and hold still for up to 10 seconds.
Can I turn tracking off?+
Not on the Sense 2 or Versa 4; on other models you can in the Heart Rate setting.
Where should I wear it?+
On top of the wrist a finger's width above the wrist bone, higher and tighter for exercise.
Does cold weather matter?+
Google says cold reduces blood flow and can hinder readings.
Does a third-party band matter?+
Loose accessory bands may stop tracking; use the band that came with the device.
What else changes heart rate?+
Google lists stress, caffeine, alcohol, illness, medication and temperature.
Does MobileTrack hide it?+
Google says the reading might not appear on the device when you use MobileTrack.
How accurate is it?+
Google has an accuracy article describing limits.