HRM 600 failed to pair but watch didn't use optical HR as backup, is there a setting i'm missing?

Ok thanks. Yeah its strange because I always leave wrist HR on so I'm not sure why it failed to switch over. I will follow those instructions.

You are correct, the "source switch" option should change automatically. Maybe the HRM lost skin contact and couldn't get a good reading but watch still had it connected and didn't change to wrist.

HRM 600 failed to pair but watch didn't use optical HR as backup, is there a setting i'm missing?

renschler said:

I did notice when I click on the HR widget, there is a setting that says "Source Switching" but it is toggled to ON already. I don't see a "Source Switching" setting within any of the activity profiles or anywhere else in the watch.

9970217 said:

You are correct, the "source switch" option should change automatically.

That is *not* what dynamic source switching does. This misconception gets repeated over and over again in the forums. I guess it demonstrates that Garmin has not explained this feature properly.

All Garmin watches, including older ones which do not support source switching, will use the wrist HR as a fallback if the connection to an external HR strap is lost (or was never made in the first place). Furthermore, dynamic source switching is only supported for certain Garmin HR straps, yet the simple fallback described above works for all external HR sensors, including non-Garmin HR sensors.

What dynamic source switching does: if your watch thinks the data from a supported Garmin HR strap is bad, it will switch the wrist  HR. This does not mean the connection (between the strap and watch) was lost, it means the connection is still active and data is still being transferred, but Garmin thinks the data itself is bad.

Also, when dynamic source switching is enabled, the watch will write 2 additional fields to the FIT file: external HR and wrist HR. (These aren't available in Connect, but you can see them with fitfileviewer.com). If you compare this to the standard HR field, you can see if and when the watch switches from external HR to wrist HR and vice versa. Furthermore, even if you use a 3rd party strap that doesn't support source switching, the watch will still write these 2 extra fields (as long as the source switching setting is enabled). In this way, you can still compare the values provided by the external HR and the wrist HR.

Of course, the fact that the external HR value is still written even when the watch switches to wrist HR (due to dynamic source switching) kind of underscores the fact that dynamic source switching has nothing to do with a lost connection to the external HR. If the connection was actually lost, there would be no data to write for that period of time.

https://support.garmin.com/en-CA/?faq=Nf8r6ApX4d9lX0G0flEsVA 

What is Heart Rate Dynamic Source Switching?

Heart rate dynamic source switching aims to provide the most accurate heart rate possible by dynamically selecting the best source of heart rate data when wearing a compatible Garmin® heart rate monitor strap with a compatible Garmin watch.

Switching sources based on the quality of the heart rate signal during an activity requires the use of a Garmin HRM-Dual, HRM 200, HRM 600, HRM-Fit, HRM-Pro, or HRM-Pro Plus heart rate monitor along with a watch from the compatible watch list below. Any Garmin HRM strap and compatible watch from the list below will do basic heart rate source switching when a heart rate monitor is unavailable (for example, if there is a drop in connection).

Ofc the support article doesn't mention any 3rd party strap will also work with "basic heart rate source switching" (i.e. when the connection between the watch and sensor is lost, the watch will fall back to the wrist HR).

Dynamic source switching is available for all activity types to provide seamless heart rate data if the heart rate strap detects low signal quality.

The biggest benefit of the feature is for running activities. A heart rate strap is usually the most accurate source of heart rate data for running but occasionally there can be inaccurate heart rate at the beginning of runs, often referred to as start-up noise.  This is caused by poor connection between the skin and the electrodes and typically resolves once you start to sweat. With dynamic source switching, when a heart rate strap detects low signal quality, heart rate from the optical heart rate sensor on the watch is displayed and logged instead. The heart rate strap remains connected to the watch and the heart rate source will automatically switch back to the strap once the signal quality improves.

Ok interesting thank you. I haven't had this issue again yet, but what's interesting is when I look at the data if fitfileviewer, I see the wrist HR and HR columns being populated until the 06:55:48 PM row. Then going forwards all HR is blank. 

Looking at the device info, that's the same time that my HR strap original paired with the watch. And the HR strap actually stayed paired with the watch the whole run, I see in Device Info it got logged again at the session end.

I'm not sure if FitFileViewer actually displays the 3rd party HR column, but would be interesting to know if that data is actually there in the file.

Records:

/cfs-file/__key/communityserver-discussions-components-files/1059/Screenshot-2025_2D00_10_2D00_12-at-12.05.12_2F20_PM.png

Device Info:

/cfs-file/__key/communityserver-discussions-components-files/1059/Screenshot-2025_2D00_10_2D00_12-at-12.04.42_2F20_PM.png

Ok looking at a more recent run with the same strap, I see all three columns in fitfileviewer. Heart Rate, Wrist heart rate, and external heart rate. So something weird happened on my run, not sure exactly bc I was wearing my watch normally, but seems like when I paired the external heartrate it messed up my OHR and the strap wasn't reporting HR data either.

Could be a bug. Even without looking at any of the data, but only going by the description in the original post, it sounds like a bug to me.

Do you remember if the built-in heart rate data field showed any data during the time that the HR strap was connected (while no data was recorded to the FIT file)? Or did it also show no data (i.e. "--")? 

thx yeah seemed buggy to me too. no i don't remember unfortunately, will see if it happens again!