How do I verify that external HRM is used?

I have the HRM-TRI and HRM-Pro. Occasionally I see at the end of an activity a message “downloading HR data”, when I know for sure the chest strap was connected at the start of the activity. This indicates to me that the connection may have been lost between the watch at some point in the activity, even if only for a few seconds.

One of the reasons I use the HRM-Pro is for this on-board memory and subsequent syncing of that data.

I certainly haven’t noticed it “flipping backwards and forwards between sensors” like DCeremuga has indicated.

There is a message that pops up the telling you that an external HR monitor is connected. Check next time but I think there is also a heart icon too that flashes initially then stays on once the strap is connected.

Provided there is nothing wrong with the strap, the battery, and it's sufficiently wet, there should be no connection issues. That is certainly my experience.

On a side note.... I tried a chest strap today for the first time, it certainly showed how unreliable the wrist OHR is. The overall min and max seem the same but the variation during the run is much more consistent with the strap.

That’s always been the case TopGuns. Optical is ok for capturing the grind of daily life but anything that involves dynamic movement and it is unreliable....from the movement itself, the weight of the watch, muscle contractions, loose/ tight strap, tight clothing, skin colour, peripheral vascular disease, cold weather etc etc. Whilst some watches are better than others, all are susceptible to these factors.

Whilst OK for your average weekend warrior, any person who values data will want to capture it in the most accurate fashion and will use a chest strap and other external sensors such as foot pods. Far from being an athlete myself, I do rely heavily on this data to measure training load, HR zones, pace, power and running dynamics. As they say in the computer world, garbage in = garbage out.....fully understanding the limitations of your tools is the first step in avoiding this.

All too often, people have too high of an expectation....a common comment here is “I’ve paid >$1,000 dollar for a watch, I expect my pace/ HR/ distance/ track to be right”. Well, not that long ago, those metrics had to be measured on much larger equipment, to get the same level of accuracy and costing >$10,000. We’re getting there but can’t fight physics with the current level of technology.

If you want the most accurate HR data you go direct to source and measure the electrical activity using a chest strap. This isn’t susceptible to most of the factors that optical is. If you really value your data, you will get one with a memory such as the HRM-Pro.

If you want the most accurate pace/ distance data, you read from accelerometers directly on the foot to avoid the inherent inaccuracies of GPS. The Stryd foot pod has a 9 axis accelerometer and a memory vs most other manufacturers 3 axis. You pay more but get more accurate data that can be synced from memory even in the event of a connection issue.

I just wish those who rant and rail about WHR would take the time to read and understand this post, and the myriad of others that say the same. Also, Garmin, Sunnto, Apple, and Polar all sing from the same song sheet with regard to the efficacy of optical heart rate monitoring from the wrist. 

There is no point beating your head against physics and physiology.

With the 235, with activity active: open menu scroll down to settings, down to sensors and accessories, find the sensor there and verify it says connected and ok.

I have noticed that sometimes I will get a "EXT HR Connected" message after I have ended my workout even though I had the external HR icon at the beginning of the workout.  I have no idea if the external HR strap disconnected during the workout or it was disconnected as a result of ending the workout for some reason. 

This alone would be a good reason to have an indication, while in workout, if the external HR is still the data source.

This "EXT HR Connected" at the end of the workout is confusing at best.

Yes. I also often get the message "EXT HR Connected" in the middle of an activity even though it seems to be connected the entire time. That is very confusing.