Good to know that I am not alone.
Seriously, I have seen all kinds of mechanisms to "take away" the screen. The latest and the most innovative one is a blue warning lamp. When the light burns, the devices must be dark.
Our now abondoned computer lab has not only screens which can be raised and lowered with motor control, also a button (software) which sends them dark!
Isn't it an irony, after the great progress we made with BYOD and other revolutions, we are reinventing old features?