Garmin HRM-TRI Review – Triathlon’s Greatest Heart Rate Monitor

Garmin HRM-TRI Review

After 6 years of usage, here is an updated (Feb 2022) and detailed Garmin HRM-TRI Review. I finally upgraded to the Garmin HRM-PRO but in some ways wished I hadn’t as I’m already on my second one. I still use my HRM-TRI for lake swimming and it must be on its 3rd battery by now but at over 6 years old it looks old, shabby and mouldy but still works!

Garmin HRM-TRI Review
Garmin HRM-TRI (HRM-SWIM) Review

I waited a while before buying an HRM-TRI. Believe me, it was difficult. This product showed the promise of doing EVERYTHING in the world of heart rate measuring for a triathlon than I had ever dreamed about (except BLE) AND a little bit more.

My self-enforced wait was because I know how difficult the implementation of HR caching underwater has been for a few other manufacturers. I wanted to make sure that the most obvious bugs had been rectified before I devoted some time on this.

This product promised and delivered s a LOT. When initially released at GBP100 (Sep 2015) this was by far the most expensive HRM on the market

The promise is for an ANT+ HRM that will cache all underwater swim HR data and later upload it to your watch. It also completes the HRV data gaps for swim data for triathletes that otherwise are generally not available. It promises to enable interval/set based HR summarises for pool sessions. Everything.

Garmin HRM-TRI Review
  • Price - 80%
  • Apparent Accuracy - 99%
  • Build Quality & Design - 97%
  • Features, Including App - 97%
  • Openness & Compatability - 95%


to Fenix 6 and Garmin Forerunner 945.

October 2020








At GBP100 for one HRM, I certainly was not going to buy both to tell me how much I need to improve my swimming. So what are the differences between the recently announced models?

  • HRM-TRI: This is all you really need from a single HRM. It will almost certainly do everything you want for swim, bike and run. Yes, it does HRV and yes it does all the HRM-RUN running dynamics – ground contact time and vertical oscillation.
  • HRM-SWIM: It’s a tiny bit better at lasting longer in a chlorine-based pool environment. It is a bit wider and, coupled with better rear suction, will stay in place when you are just doing pool training without wearing a tri-suit (or similar) to keep the HRM in place. If you’re just a swimmer you will buy HRM-SWIM. It will look sillier as it is very blue. THE HRM-SWIM WILL NOT give you running dynamics, plus I find it uncomfortable for running.
  • HRM-RUN – Identical to the HRM-TRI except it won’t cache swim workouts.
  • HRM-PRO – adds multiple, simultaneous Bluetooth connections to HRM-TRI


Read Carefully: As an ANT+ HRM it will broadcast simple, live HR data to many ANT+ devices.

HOWEVER, all the clever running dynamics will only go to a high-end Garmin Fenix/Forerunner/Chronos/Marq ie Garmin FENIX3 (HR), Fenix 5, Forerunner 935, Chronos, Forerunner 630, EPIX or 920XT all the way through to Fenix 7 and Forerunner 945.

Fenix2? 910XT? Vivoactive? No! No! and No!. Sorry. None of the clever stuff for those. But it will still work as a basic heart rate monitor just showing live heart rate over ANT+.

Unboxing – Garmin HRM-TRI Review

Garmin HRM-TRI Review

It comes in the standard-looking Garmin accessory box.

Here is a link to the manual (link to

Inside you get the HRM-TRI and an extender strap. That’s it, other than plastic bags and bits of paper.

The strap extender looks like it will work on most Garmin HRMs and is a simple and neat idea. They’ve applied the same design principle to wristwatch strap extenders. The HRM-TRI, when fully extended, will fit a chest size of up to 142cm although I would imagine you could use easily several extenders together for bigger chests.

Garmin HRM-TRI Review

Garmin HRM-TRI Review – A Closer Look At How It’s Made

The POD does NOT come off. It looks like it might if you force it but it won’t. Do NOT try!

The non-detachable pod is different from all recent Garmin HRMs and those of many competitors. Do NOT try to get the pod off. Once either the pod or strap breaks then you will have to throw it away.

However, the battery is replaceable. The blue surround easily comes off and you can unscrew 4 screws (Phillips 00) to replace the standard CR2032 battery. The cover will only fit back in one way.

The battery supposedly lasts about 300 hours. I’m not convinced, as previous pods were recommended to be removed from the strap to prolong the battery and I’ve just said that these pods cannot be removed so. (Edit: I’ve used my super-lots…maybe it did last 300 hours or even more)

As the HRM-TRI is so expensive you might probably want to take more care of it than you do with your other straps! So: Rinse daily; wash weekly use a tiny amount of detergent; and dry flat.

Garmin HRM-TRI Review
Garmin HRM-TRI (HRM-SWIM) Battery

In reality, you will never use the HRM-TRI for just running or cycling. You’d use your old strap for that. (Edit I use the HRM-TRI all the time)

Comparisons of the Garmin HRM-TRI Review

The HRM-TRI compares favourably to the competition. Whilst it is bigger than the Suunto (not shown) it is otherwise pretty small compared to the rest.

Garmin HRM-TRI (HRM-SWIM) Review
Garmin HRM-TRI (HRM-SWIM) Review 4iiii Viiiiva Wahoo TICKR-X HRM-RUN

Although you can see that width-wise it’s virtually the same as the old HRM-RUN (non-red)

Garmin HRM-TRI (HRM-SWIM) Review

On the reverse, you will see some blue material. This appears to be identical to that from which the HRM-SWIM is made. It is a bit sticky and will and does help it stay better attached to your skin. Although, as you can also see, the extra 3rd and 4th sensor pad of the latest HRM-TRI strap is NOT there. I’m not sure what to read into that.

Garmin HRM-TRI (HRM-SWIM) Review
Garmin HRM-TRI (HRM-SWIM) HRM-RUN Comparison Rear

Note well. The HRM-TRI MUST be worn the correct way up. ie with the logo facing the correct way. I suppose your heart is not central to your torso? So that may be the reason it could make a difference. For £100 I’m going to wear it the right way!!

HR Underwater – How the caching works

Simplistically it stores up to 20 hours of HR on the pod and uploads a workout’s worth at the end of your workout. Any heart rate data that is missing during the workout is appended at the end of the FIT file.

Here’s what Garmin says:

At the end of the session, the 920 receives all the stored (and time-stamped) heart rate data from the HRM-Tri and simply appends that data to the end of the .fit file. The 920 uses the data to compute some summary metrics for display in History, but the full merging of the HR data into the activity file is done offline by a HR Swim plugin on the PC side. Merging all the HR data with the rest of the activity data is computationally intensive and would be taxing on the 920 resources. It is faster for the user and easier overall to do it this way. Source Garmin via dcrainmaker

So does it append it on to the end of the swim part of the multisport file or the end of the entire fit file? (probably the entire fit file).

Moving on.

The watch seems to only look for data to upload when the SAVE OPTION has been chosen at the end of the exercise.

On Garmin’s website they state that the HRM-TRI delivers “Swim interval heart rate statistics”. My interpretation of that is that would be that you get stats updated to your watch whenever you are out of the water (BUT that is NOT the case). Garmin’s interpretation seems to be that everything is uploaded once you press SAVE and you can view the intervals later.

Indeed Garmin seems a little confused as the Int. Avg. HR and Int. Max. HR (below as an example) ARE indeed shown briefly when ‘lap’ is pressed in pool swim mode. By briefly I mean for about 0.2 seconds!

Garmin HRM-TRI (HRM-SWIM) Review
Garmin HRM-TRI (HRM-SWIM) Review

So while you are normally standing at the end of the pool it would look like this:

Garmin HRM-TRI (HRM-SWIM) Review
Garmin HRM-TRI (HRM-SWIM) Review 920XT

Not so useful.

It seems that the watch is not working as I expected either because it is allowed to display metrics that don’t work or the watch is not uploading at the end of each set/interval.

I also checked the REST SCREEN behaviour. It seems to be the same. It would have made some sense if the previous interval HR data was shown here. But it isn’t (it can’t be…it’s uploaded at the end of the session, remember!).

Finishing Up And Retrieving the Cached Data

When SAVE is pressed 3 messages are shown indicating that the 920XT SEARCHES for data, then DOWNLOADS the data and then STORES the data. The messages appear quite quickly but those are the approximate words/phrases that appear rather than the exact text.

It is possible to press stop and then press RESUME without initiating the cached HR download process. That makes sense.

No HR data is shown on the activity summary.

EDIT: It is possible to force an upload from the HRM-TRI later if, for some reason, the watch missed downloading it – I have ONLY TWICE had to use that facility, and once it didn’t work!

EDIT: Sometimes when I run or cycle it seems that my 935 has not always recorded all the HR. In such circumstances, it tries to recover the gaps in the HR from the cache. This seems to work too.

Accuracy – HRM-TRI Review

It seems accurate in what is RECORDED. HR Zones, Highs and Lows look right. I don’t intend to compare it to the HRM-RUN or to a POLAR H7. After months of usage, I’m happy is that it is as correct as a chest strap can be.

There are no unusual peaks and troughs. But then I would only expect that as the product ages.

When I have managed to record HRV data it appears to be right in the sense that it is consistent with the previous data I have recorded.

Calculations that could be based on HR such as Training Load and Training Effect and Recovery Time may well be wrong if they rely on default HR zones or run/bike HR zones. Some of these calculations look wrong to me on Garmin connect.

NOTE: I probably have over a THOUSAND hours of HRM-TRI usage. Since writing this review it was my go-to strap for personal usage and for comparison usage for this blog. Almost always the data is correct, or at least I considered it to be correct. If you check the accuracy sections of my other reviews you will almost always see the other product being compared to the HRM-TRI at some point.

Garmin Connect

On the whole Garmin Connect shows the HR data you would expect (well it did for me, others have problems with gaps in the data). For example on the exercise summary screen and then when you zoom in to the exercise itself you get something like this:


This particular session had a moving time of 40 minutes and a training effect (TE) calculated as 2.2. That seems wrong to me. I have HR zones set for RUN and BIKE but can’t seem to be able to do it for SWIM (although you can on the watch). My max HR for a swim is a lot lower than for run/bike (as indeed is my LTHR for each of those sports). So, yes, the TE may well be wrong.

Other 3rd parties such as SPORTTRACKS already allow custom zones for any sport. So my data there, from SWIM TRAINING LOAD, is correct.

NOTE: IF you check out very many other of my reviews you will see that I extensively use the HRM-TRI as my base device against which I compare various optical HR tracks. I use non-Garmin brands too sometimes. But mostly I use the HRM-TRI.


The companies most likely, in the future, to produce a directly competing and compatible swim-enabled HRM are 4iiii (Viiiiva) and WAHOO FITNESS (TICKR-X, TICKR-FIT). I would imagine that those two companies would be very close to being able to market that functionality through a firmware release if that was their chosen way forwards. I don’t know if that is their chosen way forwards.

Apparently adhering to the CACHING standard is possible for competitor products to adhere to the Garmin standard for this. 2018 sees the Scosche Rhythm 24 which claims to support that.

If you place any ANT+ HRM REALLY close to a FENIX3, EPIX or 920XT then those watches do now show (but not record) HR data in POOL SWIM or OPENWATER SWIM or TRIATHLON modes. This needs to be on the same wrist as the Garmin watch. So an HR-wrist-band like a MIO FUSE or MIO-LINK will ‘work’ in the sense that it is possible to get data to display on a 920XT underwater. However, the FUSE does not cache data in a way that is compatible, so when communication is lost then there would be no HR that the 920XT will ever be able to retrieve.

Several wrist-based optical HR watches now support HR in swimming. Notably the Suunto Spartan Sport (reviewed, link to: and Polar M430 (Reviewed, linked Although note, even as of October 2020 heart rate chest straps that cache data are rare. There is only the HRM-PRO and Polar H10 and even the latter will not properly sync back to a sports watch. Indeed almost all the swim-related innovation for heart rate has been with (inaccurate), wrist-based optical heart-rate monitors.

HRV data would only be recorded if it were created properly – optical HR is unlikely to do that accurately at present on any wrist- or arm-based device.

3rd Party Software Compatibility

Edit: This issue has now largely gone away. Because the cached HR data is appended to the FIT files many 3rd parties did not properly update their import procedures in line with the latest ANT+ .FIT file spec. I have no problems with this any more (2018)

“Why should this be an issue?” you ask.

I’m not sure. But it is.

Swim-only files that I created have problems being used elsewhere eg SPORTTRACKS, and FIRSTBEAT. (Fitfile tools is required to convert the FIT file to SDF to make FIRSTBEAT work).

I have heard others report problems with STRAVA and TRAINING PEAKS.

Triathlon-mode files seem to largely work with Sporttracks using the standard importer for SPORTTRACKS, this was fixed in 2016.

What happened: Garmin has put some extra, new and previously undocumented bits at the end of the FIT files so 3rd party software won’t work in many cases; unless specifically changed to support the product by the 3rd party.

Whilst the larger players like Sporttracks (Edit: now working), Golden Cheetah (seemingly working) and Training Peaks no doubt already have their developers on this; many other smaller companies might play a waiting game with their software updates.

Remember this will only affect previously cached data leaving the Garmin environment.

Other Points not covered elsewhere in the Garmin HRM-TRI review

  1. Using a 920XT with a MIO Link in pool swim mode: As we know the HR shows but is not recorded. At the end of a session, the device STILL looks for cached HR data for about a minute. With the MIO Link you get the message “No HRM Connection – Search Again/Skip” and then “Save Session without HR? – Yes/Search Again”.
  2. Once you have used a HRM-TRI with a 920XT it then ALWAYS looks for cached HR data whenever HR data is missing from any exercise (including RUN/BIKE…not fully tested by me). Mildly annoying but needed.
  3. So for those of you who literally want to view live HR underwater (all 3 of you) then you could maybe use 2 HRMs if the 920XT looks for cached HR data at the end of the session from the HRM-TRI to save into the FIT file. Although I doubt it would connect to a different HRM at the end of the session and I’m not going to try it! It almost certainly won’t work with 2x simultaneous HRMs.
  4. At the end of a run session where I deliberately went out of range from the HRM-TRI then I can confirm that the cached HR data was correctly retrieved at the end of the session.
  5. Following on from the previous point it seems possible therefore to, for example, start a session on the touchline of a football game. Leave the 920XT in your kit bag and play the game. At the end of the game, all your HRM-TRI data will be retrieved and saved to the 920XT. (Edit: Jun 2016 The precise nature of this functionality now appears changed since this review. Possibly due to footpod support with some hardware models. HR is certainly cached but seemingly now no other data)
  6. The 920XT *DOES* have the scope to enter SWIM HR ZONES. That might get TE/TL etc. correct on the watch and on what is stored in the fit file. However, on Garmin Connect I can only see that you could possibly change the DEFAULT HR ZONE profile to contain swim ZONES. I’ve done that but not sure if it works.


The battery lasted about a year and was simple to change. I use the HRM-TRI regularly and there has been no degradation in the strap material although it is looking like it is getting to the point where I can see that might happen. I’ve even recently managed to get some green stuff growing on the inside of the strap (nice 🙁 ). I might even wash it one of these days in cold soapy water as it has spent too much time under my wetsuit in lake water.

There has only been one occasion when I could not retrieve cached HR at the end of a session. Some Garmin devices have menu options to force a download from the watch – in the scenario I just described that worked.

2-year update: one of my straps is a bit mouldy and occasionally over-reads at the start of some exercises during warm-up. It’s on its 3rd battery.


The Garmin HRM-TRI / HRM-RUN is compatible with the metrics needed for November 2017’s Garmin Running Power release. You will need a Garmin watch with a Barometric altimeter too.

Summary of the HRM-TRI Review

It’s very expensive, although 3 years on from launch you should get one for 30% less than the retail price. I’d still say that was expensive for a heart rate monitor.

But the advertised feature set is about perfect for the Garmin environment provided by the higher-end Garmin Fenix/Forerunner watches. Comfort is great, caching is great, most of the data capture/retrieval/analysis issues seem sorted out. The advertised feature set for the HRM-PRO *IS* perfect as it adds in extra BLE connections for Zwift-type usage.

The only downside is wearing a chest strap whilst pool swimming. Scosche’s Rhythm 24 armband tantalisingly might go one better.

Recommendation: BUY – it’s my favourite Garmin product…ever

It would be great if you could help this blog in a small way and buy from one of the links below. The prices are the normal Amazon prices and I’m NOT a salaried journalist. I have a day job.

Best REI/Wiggle/PMC price is linked to. $130/Eu92/£76 and might fall in 2019.
Best REI/Wiggle/PMC price is linked to. $99/Eu75/£60 and might fall in 2019.

Reader-Powered Content

This content is not sponsored. It’s mostly me behind the labour of love which is this site and I appreciate everyone who follows, subscribes or Buys Me A Coffee ❤️ Alternatively please buy the reviewed product from my partners. Thank you! FTC: Affiliate Disclosure: Links pay commission. As an Amazon Associate, I earn from qualifying purchases.

14 thoughts on “Garmin HRM-TRI Review – Triathlon’s Greatest Heart Rate Monitor

  1. Do you know any open sourced 3rd party app that supports reading these new bits? The perl module I use hides them by default and is not able to parse the cached heart rate array.

    1. Hard question. I don’t know for sure. My understanding is that the spec is public. I know sporttracks and firstbeat are currently working on it. I imagine 4iiii and wahoo might be making their products compatible – but I’m just speculating on that last point. but in terms of ‘open sourced 3rd party app’ i’m struggling.

    2. fit file repair tool (the access one) will now ‘repair’ these cached files. I used that functionality every week and it allows the fit file to be properly saved in other formats eg I use sdf but saving to tcx I imagine would work equally well.

  2. Hi today I tried exactly what you described on point 5 during a soccer game with mixed results. At the end I got the HR data as expected, but no pace, distance, anything else. I was kind of hoping to get that info as well. Did you actually tried that out? What profile did you use for the activity? Thanks!

    1. hmm. I just tried that as well and got the same results as you in indoor running mode. Either: might have to experiment with other profiles and GPS off; and experiment with speed source. But the difference could simply be that there have been LOTS of firmware changes since then SPECIFICALLY relating to the handling of footpod data (ie alternate speed/distance source changes have def been made) which is now supported when previously it was not. I don’t have any way of easily going back to old firmware to test that. sorry. I will make a note in the review to that effect.

  3. Great article as usual. Comprehensive and very helpful. Can you advise if the HRM-TRI records HRV (RR beat-to-beat) during ‘caching mode’, and how that can be extracted?

    1. it does record hrv (Edit: IF hrv enabled on the watch – menu option on 935 but search this site for 920 instructions)
      you can only extract using a compatible watch (I treid to do the same thing myself without one using nefarious means…couldn’t do it. may be possible)
      basically compatible for tri…so that would be a 920xt, 935, fenix 3/5. that kind of thing.

  4. Thanks, I found your instructions for enabling HRV. Regarding the TRI vs SWIM, I take it the SWIM will also record HRV in the ‘caching mode’?

  5. Garmin page for HRM-SWIM, says “Stores and forwards heart rate data to compatible devices¹” being “Forerunner 735XT, Forerunner 935, fēnix 3 HR, fēnix 5/5S/5X”. But other watches have HRV function (e.g. FR620, 630). Could it work with those (cheaper and older) models?

  6. Using the Forerunner 935 “Triathlon” mode, if I was to swim, then hit the next button which changes the swim to “Bike” mode, will my HR data be live or will it continue storing the data until after the race? I can’t seem to find anywhere that tells me this. I don’t want to have to press stop after the swim discipline then start the bike mode during a race just to get live HR data during my ride.

    1. yes it will store the entire race. the 935 almost certainly will do all things tri ‘properly’ by how almost everyone would define that.

      enable transitions. press lap going into transition. lap going out of transition. it will work correctly.
      if you mean will an AVERAGE HR roll over to the next sport…then, no, it wont do that. there might be a ‘total multisport metric’ but i dont think so from memory

Comments are closed.