Garmin Fenix and external heart rate sensors

All external heart rate sensors can be used without wearing the watch, however you need to keep them close, unless you use the HRM-Pro or HRM-Tri. These two have the ability to upload hr data to the watch post-workout.

Thanasis Merkouris said:

I am between Garmin HRM Pro and Polar OH1+ ( I think the Polar would be more comfortable).

Yes the Polar will almost certainly be more comfortable on your arm than the chest strap and the OH1+ is almost certainly going to be less expensive than the HRM Pro (but other, less expensive, chest straps might suit anyway).  That said, I would offer caution using any OHR sensor that is anywhere on your arm for strength work.  My experience with the Scosche OHR band (very similar to the OH1+) is that, whilst it is far superior to anything built in to a watch for endurance activities (running, cycling, etc.), for strength training it was utterly useless; not just exclusively arms/upper body isolation either, barbell squats and deadlifts would completely throw the OHR sensor.  I've only ever found a chest strap reliable for strength work, so couldn't recommend anyone use anything else (even Polar acknowledge that here under the OH1+ Cons "Not necessarily accurate in sports where you move your hands vigorously or flex the muscles and tendons near the sensor").

The advantage of the HRM Pro (or HRM Tri for that matter) over other chest straps, is you can start the activity on your Fenix 6, then leave the watch in locker/bag/car, exercise with just the strap on, then the cached HR will download to the watch when you stop the activity at the end (known as 'store and forward').  You do need to start an activity on the watch for this to work; although the HRM Pro (but not HRM Tri) will fill in any blanks where you aren't wearing the watch, on your 24 hour HR stats in Garmin Connect, if you accidentally forgot to record an activity on the watch.  If you don't need the store and forward capability (you wear the watch when exercising), then a less expensive chest strap (HRM Dual, HRM Run or Polar/Wahoo equivalents) may be entirely fine; all will connect with the Fenix 6 via ANT+ and/or BLE to give live HR during the activity. (Also worth noting that the Polar OH1+ equivalent to store and forward isn't compatible with Garmin devices, in case that was something you assumed would work.)

So, the right choice for my case is HRM Pro.

What different has HRM Pro from HRM Tri?

Also, is there any other similar device to HRM Pro?

Thanks for your help!

Both do store and forward, are suitable for swimming and have running dynamics (which is also required to make the Garmin Running PowerCIQ app work). The key difference is that HRM Pro transmits/receives both over ANT+ and BLE, whereas the HRM Tri only covers ANT+.  The BLE capability of the HRM Pro means you can pair it to smartphone/tablet apps, such as Zwift, as a HR monitor.  That also means that the HRM Pro can pair with your smartphone and communicate directly with the Garmin Connect Mobile (GCM) app, to transfer HR and steps for periods you aren't wearing the watch and also means software updates for the strap can go direct from GCM to strap (rather than GCM/Express to watch to strap).  The HRM Pro is (currently) the most feature packed HR strap out there, if you're in the Garmin ecosystem, but you do pay a little extra for that full package of functionality.

Thanasis Merkouris said:

What different has HRM Pro from HRM Tri?

• HRM-Pro supports BLE connection, the HRM-Tri does not.
• HRM-Pro can work without a watch for recording fitness data, can connect directly to the Garmin Connect mobile app.
• Provides cross country skiing power for compatible watches.
• Shows battery status when viewing activities in garmin connect.