@dusx thanks a lot - all sorted! cheers, Dave

@bennnid said:

I begin to understand the power of activated scenes ;-)

 You can also use background Scenes to make global projection mapping easier: https://community.troikatronix.com/topic/5495/global-projection-mapping-simple-show-template?_=1613735987660

@whatnao You could also run the projector in an activated scene with a keyboard watcher that listens for a trigger and toggles the projector on or off - so the movie keeps running and the projector is what goes on or off. Since the scene is active the keyboard watcher will react even if you are currently in another scene.