They’re not really that expensive though. I think you could get fully trained for well under $100? That’s the price of one class anywhere else, often more.
I think one of those rotary yellow lights would be a blatantly obvious signal without being obnoxious. It could maybe turn red when it’s jam packed and absolutely needs to be emptied, and maybe that’s when the universal kill switch would be engaged. But as someone else said there’s a fair bit of risk when your machine shuts off suddenly. Could certainly ruin some nice lumber that way or risk it being thrown by the router or table saw suddenly changing speed of the blades.