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Auxiliary Heart Rate


A simple data field that connects to ANT+ heart rate monitors, displays heart rate (in bpm), and records it into the FIT file.</p><p>This was developed so that I could use the built-in optical heart rate monitor on my Forerunner 235 and an external ANT+ chest strap at the same time, logging values from both for comparison.</p><p>Note that you should not have the external ANT+ heart rate monitor paired to the watch in the usual fashion, the data field will make its own connection.

What’s New

Version 1.1 added the ability to set the ANT+ ID of the external heart rate monitor you wish to connect to. Set it to zero (the default) to search for any HRM (it will select the strongest signal, probably, once connected it won't switch to another HRM).


Companion Hardware

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Additional Information


This app requires access to:

  • Send/receive data via ANT radio to/from third-party sensors
  • Record additional information into activity files
  • D2™ Bravo D2™ Bravo
  • D2™ Bravo Titanium D2™ Bravo Titanium
  • D2™ Charlie D2™ Charlie
  • D2™ Delta D2™ Delta
  • D2™ Delta PX D2™ Delta PX
  • D2™ Delta S D2™ Delta S
  • Descent™ Mk1 Descent™ Mk1
  • Edge® 1000 Edge® 1000
  • Edge® 520 Edge® 520
  • Edge® 520 Plus Edge® 520 Plus
  • Edge® 820 Edge® 820
  • Edge® Explore 1000 Edge® Explore 1000
  • Edge® Explore 820 Edge® Explore 820
  • ForeAthlete® 230J ForeAthlete® 230J
  • ForeAthlete® 235J ForeAthlete® 235J
  • ForeAthlete® 630J ForeAthlete® 630J
  • ForeAthlete® 735XTJ ForeAthlete® 735XTJ
  • ForeAthlete® 920XTJ ForeAthlete® 920XTJ
  • Forerunner® 230 Forerunner® 230
  • Forerunner® 235 Forerunner® 235
  • Forerunner® 630 Forerunner® 630
  • Forerunner® 645 Forerunner® 645
  • Forerunner® 645 Music Forerunner® 645 Music
  • Forerunner® 735XT Forerunner® 735XT
  • Forerunner® 920XT Forerunner® 920XT
  • Forerunner® 935 Forerunner® 935
  • fēnix® 3 fēnix® 3, quatix® 3, tactix® Bravo
  • fēnix® 3 HR fēnix® 3 HR
  • fēnix® 5 fēnix® 5, quatix® 5
  • fēnix® 5 Plus fēnix® 5 Plus
  • fēnix® 5S fēnix® 5S
  • fēnix® 5S Plus fēnix® 5S Plus
  • fēnix® 5X fēnix® 5X, tactix® Charlie
  • fēnix® 5X Plus fēnix® 5X Plus
  • fēnix® Chronos fēnix® Chronos
  • vívoactive® vívoactive®
  • vívoactive® HR vívoactive® HR
Average Rating: (24 Ratings)

December 30, 2020 | Version 1.1.0-u-upd8

Simply perfect. Thank you

April 12, 2020 | Version 1.1.0-u-upd8

Hi, thanks a lot for this simple and great app! It works perfectly on my FR235, and I use it to compare the built-in heart rate sensor with the external strap. Would it also be useful to make it compatible with the Vivoactive 4S? Many watches are supported, but unfortunately this one is not in the list. I would like to also compare the built-in heart rate sensor of that watch with my external strap. Thanks in advance!

Kristen Wangerin
February 14, 2020 | Version 1.1.0-u-upd8

Cool! I look forward to playing with this data more. For others out there, I got this to work most easily (on my Mac) using fitdump: 1) Download fitdump and GarminFIT packages. 2) Extract both. 3) Put the Fit file you want to read as well as the Garmin folder (which will contain the file in the same directory as the fitdump execuable. This way fitdump will find Garmin::FIT. 4) Run: ./fitdump

Chris Dunhill
April 19, 2019 | Version 1.1.0-u-upd8

Can't get this to work. Fenix 5+, latest firmware updates. Unpaired Polar HRM, added the ANT+ code (AND tried with 0) but data field just says "searching". Am I missing something?

Developer Reply
December 19, 2019, IMGrant

I don't think Polar HRMs are ANT+?

Bruce Tiller
January 10, 2019 | Version 1.1.0-u-upd8

Great app - it allowed me to directly compare wrist based measurement on new watch (Forerunner 235) to chest strap i have worn for last couple of years. They compared very well in my case and it gives me more confidence in the watch going forward. Thanks for a very simple and useful tool!

Dragan Music
August 6, 2018 | Version 1.1.0-u-upd8

Excellent app!. The athlete was concerned when switching to new FR645 as the data seemed different from FR630 + Miolink (thought it was faulty!). Was able to show the correlation and difference and turns out it was different but still OK. Big relief. Will continue to monitor over different session types to get an understanding of FR645 characteristics. Thanks for the app!

March 16, 2018 | Version 1.1.0-u-upd5

This is a great app for recording and comparing multiple HR monitors. The ability to input a particular ANT+ ID is a great addition.

Sergio Ibáñez
January 16, 2018 | Version 1.1.0-u-upd1

Really useful to compare OHRM with band... Congrats!

December 6, 2017 | Version 1.1.0-u-upd1

Can you help me? I really don´t know how to use it together, OHR and Chest strap. :(

October 22, 2017 | Version 1.1.0-u-upd

Very helpful for comparing OHR to a HR strap!!

September 30, 2017 | Version 1.1.0-u-upd

Found this through the forum. Thanks to all. Heart rates at rest are correct to the beat, but I suspect while running the wrist one is off (by 10 bpm). With this app and data screen I added to Running activity I will check it easily.

Neil catley
September 12, 2017 | Version 1.1.0-u-upd

Very very useful to compare the 935 wrist HR with my Rhythm+. Would it be possible to release a second version of this, with a slightly different name, to allow capture of a third HR field ?! I could then compare wrist, Rhythm+ and a chest strap!

Kenny Baldo
September 10, 2017 | Version 1.1.0-u-upd

Got to say this is a great tool to compare your HR strap to the OHR from your watch. Easily set screen to show both current HR on one screen. I'd like to see a display option for avg lap HR. After several uses. Plus data shows up on GC where you can easily overlay to compare one to another. After several runs the overlay is almost identical with a 2 bps differential on avg HR and 1 pt on Max with strap being the lesser # of the two. This has been tested on various runs, locations, paces and elevations with the Garmin 935. Only thing yet tested on is on intervals where HR spikes will occur and likely the 935 will be substantially off, but maybe the avg works out to the same. We'll see this week.

July 27, 2017 | Version 1.1.0-u-upd

Where can I find my heart rate display on my device?

Wolfi L
July 26, 2017 | Version 1.1.0-u-upd

Great App, works as it should and allows me to record HR during swim with my Mio Link.

July 14, 2017 | Version 1.1.0-u

Thanks for this - works perfectly. Would it be possible to also show the optical heart rate reading on the same display page, for instant comparison? Thanks

July 3, 2017 | Version 1.1.0-u

Great data field for allowing you to work how best to wear your garmin to get a decent optical heart rate reading, by comparing it with a chest strap monitor. Nice one!

Peter Holloway
May 31, 2017 | Version 1.1.0-u

Perfect for comparing OHR and chest strap performance. The graph and stats are also displayed in Connect IQ after the workout has uploaded. Thanks!

May 27, 2017 | Version 1.1.0-u

it's not working on my FR 935. The screen shows "searching" and the optical senzor is not on. it worked very good on my FR 235..

April 24, 2017 | Version 1.1.0-u

Great! Thanks a lot for this! I don't suppose it's possible to also detect when a strap is enabled on/by the watch and then fish up oHR as aux instead?

April 10, 2017 | Version 1.1.0-u

Does EXACTLY what I was looking for. However, I would like to be able to access the actual raw data, to be able to extract the Auxiliary heart rate data and compare it up closer. the Connect IQ additional .FIT info is gone when exporting to .TCX and golden cheetah imports the .FIT without the 2nd HR. any recommendations from the Dev?

Developer Reply
April 20, 2017, IMGrant

You'll need to download the original FIT file from Garmin, and use tools such as FIT2CSV (from the FIT SDK) or fitdump (from the python package, fitparse), or write your own code to extract the records from the FIT file.

Darren Croton
April 5, 2017 | Version 1.1.0-u

Works great. Thanks for this!

Lorenzo M.
February 24, 2017 | Version 1.1.0

Fantastic, this le t me see my son freq during training!

Developer Reply
February 25, 2017, IMGrant

That's an excellent use case I hadn't thought of!

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