Fitbit Sense capture heart rate when not wearing it

[mbarylski]

Shouldn't the watch know that I'm not wearing it or do I need to disable something every time I take it off? My heart rate was recorded at 120 when I wasn't wearing it.

Moderator Edit: Clarified subject

[AlvaroFitbit]

@mbarylski It's great to see that you've visited the Fitbit Community!

Let me help you with your Fitbit Sense recording heart rate when you weren't wearing it. This is odd. Does the heart rate reading shows for a long period? Remember that your graph shows your heart rate in 5 minutes intervals so the data could have been for a 5 minutes period that had partially recorded data. Still I suggest you clean the back of your device with cotton and rubbing alcohol and restart it. Turn the heart rate off, save and sync then turn it on save and sync again. Also check these tips to improve the heart rate reading.

I look forward to your reply.

[Lioslaith]

I have had the same issue with my Sense. I was in the hospital for 7 days, not wearing my sense, which was left face down on my bedside table, and I came home to a weeks worth of HR readings that jump rapidly from normal to insanely high. Is there a better way to fix this issue? Is it a bug in the software? Can I delete the data for the days when I know the data is wrong?

[sockatume]

This is a known issue with basically every consumer-grade optical heart rate monitor. There's a good article on it here:

https://www.wareable.com/fitness-trackers/why-heart-rate-monitor-work-on-toilet-rolls-6606

The data that these consumer-grade sensors produce is fairly noisy and inconsistent, so a fitness monitor can't just measure your actual pulse and report that information. Instead the Fitbit has to use a model of what your pulse is supposed to look like, adjusted using the signal from the sensor, to basically guess what your heart rate is. The down side of this is that if the watch knows it's sitting on top of something, but it's not actually detecting a pulse, it assumes it has made a mistake and desperately tries to come up with a result. More often than not it will find some tiny bit of random noise in the signal that fits its model, and proudly declare that it's found a heart rate.

It wouldn't be completely inaccurate to say that the Fitbit is hallucinating a pulse because it's being deprived of information for too long.

Only a few very expensive smart watches, or actual professional-grade heart rate monitors, avoid this problem. The only real way to avoid it is to keep your Fitbit face down, on the charger, or turned off, when you're not wearing it.