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9.33/9.36 has ruined heart rate monitoring!


After upgrading my my fenix 7 to 9.33 I have noticed a few odd things about the heart rate that's displayed/recorded on my watch. Here's what I noticed:

First run with the new Firmware: My old H7 chest strap sensor, which worked fine before, showed sudden drops in HR of about 30 bpm while running at a constant pace. (H7 has a fresh battery.)

I thought was just the chest strap, but then I noticed sudden mayor changes in HR with the integrated HR sensor as well, when I was just at home. Within 2 seconds it jumped or dropped by about 20 bpm.

Also, when I stand up after sitting for a while, my heart rate does not change at all on the watch. It keeps showing mid to high 40s. However I can clearly feel that it's way off for about 15 to 20s and then it starts "catching up". > Again I big jump in HR on the watch. I tested this multiple times by comparing it to the data from my H7 + old watch where it behaved as expected – a gradual increase in HR.

I also restarted the watch which didn't help and I made sure I was wearing it correctly. (I wore it the same way before upgrading the firmware.)

Before the upgrade it felt very reliable and now I don't know what to think. Has anybody else noticed something similar? Any suggestions on what to do now?



  • Anyone else who has the HR problem since 9.33/9.36 and has tried downgrading to 8.37 to see if it fixes the problem? After I downgraded I'm still having the same problem, while before I installed 9.33 the HR was good with 8.37. Support is suggesting it might now a hardware issue. I'm still hoping there will be a software fix, but I was wondering if anyone else had downgraded and still had the problem.

  • After I downgraded I'm still having the same problem, while before I installed 9.33 the HR was good with 8.37.

    Did you downgrade the Sensor Hub firmware too? That's the part that is the likely to be the culprit. If you have SNS v20.06, then you need to downgrade it minimally to 20.04, if not earlier. Check the older alpha packages for the matching file: 

  • Here is an example of what started about a month ago and what I now see regularly:

    Here you can see HR going up by about 30 bpm within 30 seconds without any change in effort on my side. I was running slightly downhill at a relaxed pace. My HR was in the 130-135 range. Then suddenly I see the HR at about 165. Once it was there it didn't want to go down until I stopped completely. On the graph you can see the HR against the grade adjusted pace. The watch was strapped fairly tight but not super tight. 

  • As I see there is new Beta version but nothing mentioned there about this problem, any update on that issue ?

  • I want to update my case: after contacting Chris privately and Garmin support, they advised me to upgrade to v 9.37 and do a master reset. I did that, today I tested the watch and it still has problems with HR.

    This is the HR detected in today's bike ride with the v 9.37 and master reset, you can see very well the drops in bmp especially in the center of the activity.

    This is the exact same bike ride made time ago with v 8.21, same watch, positioned and tight on the wrist the same as now.

    The difference is absurd. Before the new v9.. software there was no such problem. It happens to me only with the bike activity, and only from the latest v. software. For now I am waiting to ask for a repair / replacement because in my opinion they can solve via software. I wait the next version, if it still does not work I will appeal the warranty

    They can fix it, it's software. I also do strength training with pull up push up lots of movements, sometimes it struggles and detects late bpm, but at least it detects them. On bike activity it goes very badly, and it has less stress than the strength training I do

  • Thank you for your update on the v9.37 software.

  • Hi Chris, I've been having what I *think* is the same problem Aleph is. I can't recall exactly when it happened, but sometime in the last several weeks (couple months?) I noticed a dramatic degradation in the performance of my Fenix 7 heart rate monitoring after an update. The problem is very similar to one I had awhile ago with the Fenix 6 (which had been fixed after an update). It seems like the watch is 'locking on' to my cadence intermittently. My heart rate goes from 140s-160s to 80s to 90s after no significant changes in effort. It stays there for up to several minutes. If I intentionally turn my wrist and point the bottom of the watch away from my body I can sometimes get it to lock back onto my pulse.

      Restarting the watch doesn't help. It is definitely related to a software issue (fine for a few months, then consistently failing after an update...probably 9.33 but can't recall - just recall updating and noticing this on the ride after). I can't begin to tell you how frustrating it is to see this problem again. I use my watch as my primary HRM, and the Fenix 6 (after the fix) was so good...then the Fenix 7 was good for a few months after I purchased it only to be ruined. Please fix this, then leave it alone - it worked so well!

    Sincerely, Brian Theyel

  • I recently got a Fenix 7X and have been wearing both it (left arm) and my FR945 (right arm) to compare. I've noticed numerous instances of the Fenix 7X reading higher wrist heart rate than the FR945. Each time the FR945 reading is in line with what I expect for the effort; in cases where I was walking, I manually took my pulse and verified that the FR945 was indeed accurate and the Fenix 7X was often 20-30 BPM higher. I trust the FR945.

    Both watches have been worn very tight on the wrist during activities (1-2 notches tighter than in everyday use).

    For recorded run activities, below is the most egregious example:

    Another example that was mostly good but had one noticeable spike in the Fenix 7X data (an easy slight downhill where the FR945 correctly measured a small drop in HR):

    After the really bad recording on Oct 25, I decided to downgrade the Fenix 7X to 8.37 and see if it made any difference. I'm not sure if it did. Both runs since then have had noticeable spikes somewhere in between the Oct 18 and Oct 25 examples above. With firmware 8.37, Sensor hub is 18.02 and WHR is 7.00.00.

    The last one interestingly has one instance of the Fenix 7X reading noticeably lower than the FR945, so I'm not sure which is more accurate in that area.

    I also have numerous walking activities that I haven't gone through to compare yet, but as mentioned above I have noticed discrepancies there as well.

    This is definitely disappointing as the Fenix 7X is very expensive compared to the FR945, which was rock solid for multiple years! I will contact  tomorrow to provide direct access to the above data.

  • Hallo ,yesterday I was running with the Garmin HRM Dual and the heart rate showed complete nonsense, about 30 beats higher. It continued even after disconnecting the chest strap and taking measurements from the watch. Garmin Fenix 7X, software version 9.37.

  • In an activity like running a watch like the fenix 7x, with its size and weight, may be less stable on the wrist than a bit smaller and lighter Fr945. However, it‘s evident that the bpm readings are much more similar to the 945 with the "old" software on the 7x.

    I also gave Chris access to the data to investigate the issue. I think it's useful feedback to work on the problem.