A Garmin Forerunner 965 that shows a wrong heart rate, with a number far too high, too low or stuck, has an optical sensor reading that is being disturbed, and the causes are about fit, skin and conditions far more often than a faulty watch. The Forerunner 965 is a running and triathlon watch with an AMOLED display and Garmin's wrist heart-rate sensor, which shines green light into the skin and reads the changes in the blood flow.
The checks in more detail
The result can be wrong if the watch moves, if the light does not reach the skin well or if the signal is confused by the pattern of the arm's movement. Start with how the watch is worn. Wear it about a finger's width above the wrist bone, snug enough that it does not slide but not so tight that it cuts the circulation. For a hard run, tighten it a notch, and loosen it for rest. Clean the back of the watch with a damp cloth and dry it, because sweat, sunscreen and lotion block the sensor, and clean your wrist too.
Dark tattoos on the wrist, skin of certain types and a cold wrist reduce the reading, so warm up and consider moving the watch to the other wrist or higher on the arm. Then the settings. Check that Wrist Heart Rate is set to On in the watch's Health & Wellness settings, not to Off or Broadcast only. Update the watch software, since Garmin refines the sensor's algorithms. If the heart rate is wrong during intervals, that is a known limit:
the wrist sensor can lock on to your running cadence, so the displayed rate follows the steps instead of the pulse. Pair a chest strap, which is much more accurate for fast changes, with the watch in the sensor settings. Compare with a manual pulse count to test. Restart the watch if the reading is frozen. If the numbers are wrong at rest with a good fit, a clean sensor and updated software, contact Garmin with the model and serial number, and ask about the sensor.
Differential
Likely causes of “Garmin Forerunner 965 heart-rate readings are missing or inaccurate”, and how to tell them apart
- 1
A loose or misplaced watch
What separates it The reading jumps or lags
How to confirm Wear it snug above the wrist bone
- 2
A dirty sensor or sweat and lotion
What separates it The reading is erratic
How to confirm Clean the sensor and the wrist
- 3
Cadence lock during running
What separates it The rate follows your steps
How to confirm Use a chest strap
- 4
A cold wrist or a tattoo
What separates it The reading is low or missing
How to confirm Warm up or move the watch
- 5
A setting off or old software
What separates it No reading appears
How to confirm Turn on Wrist Heart Rate and update
Before you touch a setting
Record this first — changing settings destroys the evidence
- When the reading is wrong: rest or exercise
- How the watch is worn
- Whether Wrist Heart Rate is on
- The software version
Try in this order
0 of 6 completedAdjust the fit
ReversibleSnug above the wrist bone.
Clean the sensor
ReversibleAnd the wrist.
Check the setting
ReversibleWrist Heart Rate on.
Update the software
ReversibleOn the watch.
Pair a chest strap
ReversibleFor intervals.
Contact Garmin
ReversibleIf it stays wrong.
Model-specific
What is true of this model and not of its siblings
- The optical sensor
- Green light reads blood flow at the wrist.
- Fit
- A snug, steady fit matters most.
- Cadence lock
- It confuses running and pulse.
- A chest strap
- It measures electrical signals.
- Updates
- They refine the algorithm.
- Garmin help
- Quote the model and serial number.
Stop boundary
When this stops being a self-service repair
- !Do not ignore chest pain or dizziness; seek medical care
- !Do not rely on a wrist reading for medical decisions
- !Contact Garmin if the sensor never reads
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Why is my heart rate wrong?+
Fit, dirt, cadence lock or conditions.
Is a chest strap more accurate?+
Yes, for fast changes.
What is cadence lock?+
The sensor follows your steps.
Does a tattoo matter?+
It can reduce the reading.
Should I tighten the strap?+
For hard efforts.