[nickr]

But I thing that looking for acual GUI mode is "the right way". Unfortunately, I was unable to find anything relevant to "bind a listener/observer to settings changes". Could somebody point me how to do it? Some example/some addon which is already using this feature/anything/...

Thanks a lot!

There is a plugin for philips hue lights that (as far as I can see) polls regularly to see if there is anything playing (and if so switches your lights off). You might look at the logic there and see if there is a similar way to see if a 3D video is playing.