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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?



  • Hi Michael, same here (model Fenix 7S Solar). HR monitoring got just plain unreliable.

  • Good to know, thanks! (7X SS here btw.)

  • Hi,

    I also notice same weird behavior since 9.33 update. My chest strap was drying in my bathroom as I do since always, and now my watch randomly detect it during the night! So I'm stuck with a max of 226 bpm for my day charts :-/

  • Uh, that didn't help your sleep score, I guess. ;)

    Yeah, something is up. I also had to remove my H7 completely from the fenix 7, or it would keep recording data from it. (I had the sensor removed from the strap)

    But the weird jumps continued regardless.

  • A surprising 93/100, I found out this during my morning Health Snapshot where my HR was at 130 bpm lol

  • Here is some additional data.  I hope it helps.

    Both of these charts are a 35 minute elliptical workout.  It's a random resistance program that changes every minute.

    Polar H9

    Fenix 7 Sapphire Solar 9.33

  • Quite the difference! Thanks for the data! (Had to look up Elliptical ;) )

  • Not sure if this is relevant, but here are two 10 min. segments of two subsequent runs. Red is old firmware, blue is 9.33.

    I overlayed the graphs, scaled them vertically to roughly match the range and changed the color of the newer one.

    It seems the 9.33 graph has a lot more "flat" areas, whereas 8.39 seems smoother and more detailed which could mean that it updates more often.

  • My chest strap was drying in my bathroom as I do since always, and now my watch randomly detect it during the night

    I think this is a different issue.  What you're seeing is the chest strap signal being detected by the watch and then the watch using that data over the optical HR.  The chest stap is for some reason sending a signal that is the max value. In an ideal world the chest strap shouldn't broadcast, but this can and should be fixed on the watch side as well.

    The software on the watch should have intelligence enough to know to ignore max/min/invalid data from the chest strap especially when it it receiving a signal from the built in optical heart rate.  See bug:

  • Oh great. So I guess I won't be updating. Garmin, how come all those errors keep on popping up?