Does watch HR sensor also record if heart rate strap is connected? (HRM-Dual & Fenix 8)

Ahh, good point.  The switching is an setting option on the F8 watch itself, so I assumed it was doing this.  I might call garmin support on this...

megaphylls said:

Is the hrm dual enabled for this? I do not see it in the list

If you mean the comparison of the HR data from the internal and external sensors in Ftifileviewer, mentioned in the post you are replying to, then it is apparently available with HRM-Dual too, since the screenshot from net1994 on the first page of this thread, shows a chart with two separate and different curves from the internal and external HR sensors.

The final resulting HR curve can be plotted too, and there you can easily see whether and where the internal OHR was used. No need to ask the Support. I suspect that the average support person will not know it anyway.

I meant that since it was not listed, I wondered if there were any side effects of using it (erroneous data, etc.). I was interested in trying it but gave up when I read that HRM-Dual was not listed. Glad to see it's ok instead!

Since I have no HRM-Dual, I cannot confirm that the Dynamic Source Switching can be used with it. I am just telling that you can compare the internal and external HR signals, even if you use HRM-Dual, regardless whether the source switching really works or not.

However, if you have that strap, you can see it quickly by comparing the graphs 'heart rate' vs 'wrist hr' and 'heart rate' vs 'external hr'. If some parts in the resulting 'heart rate' differ from the 'external hr' and are identical to the 'wrist hr', then it was caused by the source switching.

ok got it! thanks for your kind insights!

trux said:

Since I have no HRM-Dual, I cannot confirm that the Dynamic Source Switching can be used with it. I am just telling that you can compare the internal and external HR signals, even if you use HRM-Dual, regardless whether the source switching really works or not.

Yeah I've found that even with a 3rd party HRM like Polar H10, my FR955 (which supports source switching) will stil record both "external heart rate" and "wrist heart rate" to the FIT file at the same time (along with "heart rate", which is always recorded).

This is despite the fact that:

- Garmin clearly says that source switching is a feature that only works with supported Garmin straps (which kind of implies: definitely not 3rd party straps)

- Garmin won't allow the source switching feature to be toggled if Polar H10 is connected (as opposed to one of the Garmin straps on the list)

So I think the best way to determine whether source switching is truly supported for your strap is to try to toggle the option in your watch's settings. If you can't toggle the option, then your watch is not supported (*). I do think there's a good chance that HRM-DUAL is *not* supported, because the support article does not mention it, and the HRM-DUAL is a couple of years older than the other straps.

(*) unfortunately there is a bug with some beta firmware for other devices where people are unable to change the source switching option, even with a supported strap connected.

I do think this behavior of recording both wrist and external hr even for "unsupported" straps brings up a few issues:

- one of the motivations for disabling source switching is to save battery life by ensuring the optical HR is turned off when using an external strap. But it's turned on by default, and you can't turn it off with an unsupported strap. Furthermore, you hypothetically won't get the primary "benefit" of source switching in this case (the part where the watch will use supposedly higher-quality data from the strap instead of the OHR)

- this is yet another demonstration of why it was a bad for Garmin to tie the ability to change the source switching option to having a supported strap connected. The option is enabled by default, and apparently having it enabled does make a difference even when you use an unsupported strap

- is this a bug? kind of seems like an unintended consequence - why leave the OHR turned on just to support source switching when source switching supposedly won't work?

In fact you do no have to rely on the option of source switching. You can simply disable it by using the Jacket Power Mode in the concerned activity, which turns off the WHR sensor, hence the watch is forced to use the external HRM alone.

I know this is the Fenix 8 forum, but not all devices have jacket power mode. (Forerunner devices, such as my FR955, do not). Yes, even Forerunners have a battery saver mode, which allows you to select certain features to enable or disable, including wrist HR, but that's not a great workaround - if the user is already using battery saver mode to get extreme battery life by disabling several features (which is how it's configured by default), they may not want to reconfigure it to only disable the wrist HR and nothing else, just for activities. The worst case scenario is that they'd be constantly reconfiguring the battery saver mode, which is impractical.

I mean sure, another workaround would be to disable to wrist HR manually before doing an activity with an external HRM. Then you'd have to manually re-enable wrist HR when you're done. Maybe a bit more practical, but still pretty annoying.

Regardless of any viable workarounds, my point still stands that if an option *does something* when enabled (like forcing the OHR to stay on), it's arguably incorrect to disallow the user to disable it on the grounds that the option isn't *fully functional* (because a supported chest strap isn't connected).

That's why I think it must be a bug that source switching "half works" when an unsupported chest strap is connected. It's either an oversight or a terrible design decision.