How to disable external HRM for some activities

I'm a little confused about your question. If you don't want your Tri connected for pool swimming, don't wear it. If it's a case where it's nearby and trying to connect, go into settings, sensors and select disconnect for the Tri. You'll have to turn it back on if you want to use it for other activities. 

I'm not wearing it.
the Fenix expects it to be there so it doesn't record HR off the optical sensor (may be worthless I know) and searching for the saved data which doesn't exist when I save the workout.
I was hoping to avoid having to continually disable/enable the sensor, and just turn it off for all pool swims

What is your setting for wrist heart rate, while swimming?  I thought the default was set to on, but I may be mistaken.

It's supposed to work the way you're wanting it to - it will use the WHR by default unless it detects an external sensor. If you don't want to use the chest strap, then just don't use it, and the watch will revert to using WHR by default. So you must have some other setting causing it to not behave that way, like Tess is suggesting. Like you may have the HR turned off entirely for the Swim activity.

Hi Ken, 

Did you ever find a solution to this issue? I have the same problem. Wrist HR is turned on for swimming and I never wear the strap to swim - not once. The watch still looks for it and causes extra steps to make sure the workout is saved. 

Gale 

I have same issue; a bit annoying as you have to tell the watch not to look for HR from strap before saving

Exactly. And if I get distracted (like collecting gear and taking a shower) it loops back to the main screen without saving. 

nope.  I never did find a solution.  Just dealing with the annoyance.

Well darn. Thanks for the response.