Reading through the forum it appears GARMIN still has NOT implemented a switch to remove out of zone warnings despite it bothering many people. I am happy with any solution to a problem that I would consider is quite common:
I have a bike with a power meter, but do regular indoor workouts. When the Garmin Edge 840 connects to the smart trainer it almost always picks the power meter of the bike. Even though Garmin controls the smart trainer at a given power for the workout I get constantly out of zone warnings (as the power meter shows fluctuations). So it seems the only solution I came across is to switch of audio warnings altogether (which seems like a terrible solution), or I remove the power meter once I train indoor and add again when I ride outdoor.
It renders the 840 basically unusable at this point, such that I ended up using my phone and an external app to control the workout and let the edge device simply record.
I cannot understand why garmin does not:
1) Implement a switch to eliminate out of power zone warnings
2) Provide a switch to choose between power meters
Both of these are much more useful than the other changes the made lately (whatever group ride features that they implemented which are much more complex!)