garmin usually allows you to delete sensors in the setup..cant see the straps being any different.

I should have asked a better question.

Can I default to the strap.....or Scoshe (in lieu of the optical)?

(From my experience with the 735XT) If you pair an external HRM with the watch it'll be preferred over the built in optical. Don't know what happens if you pair both a HRM-Tri and the Soche at the same time. The HRM-Swim is what I'd call awkward at best - I have one from when I bought the 920XT bundle and basically don't use it (it's super wide, I personally have trouble keeping it on/comfortable for a full session, and it increases your dork factor 1000x).

Depends on the device. For example an Edge 510 only connects to a single HR strap. You have to search for a second one. 910XT same I think.

Fenix 3 can have multiple sensors queued. If only one is available to connect to, it'll connect to that fine. However if it can find both it often won't connect to either. This is the same for any type of sensor, power meter, spd/cadence etc. I use a HRM-RUN and a scoshe. So can't help you on the swim HR side.

Do any of the units you mention have an optical HR sensor?

I'm asking what happens if you have a unit (let's say a Fenix 5) with optical HR......and you want to use the HR strap (any HR strap that is compatible).

Does the HR sensor over-ride the optical? Which does the unit default to? I'm hoping it would connect to the sensor and that would over-ride the optical, but I don't know that to be true. Ideally, it would switch to optical if it lost signal with the sensor. But, I don't know that, either.

Mine is the fenix 3 hr. So if it doesn't connect to a sensor it defaults to the inbuilt optical. But external sensors do override the inbuilt.

However during swimming the inbuilt isn't used. But i believe the fenix 5 hr will do swim hr soon. Check dc rainmaker.

Not sure what happens if the external sensor dies mid activity.

Thank you.