In our elementary school cafeteria, we had a large traffic light that was sound activated.

Reasonable noise levels were green, but if we got too loud it would turn yellow to warn us to quiet down, but if it turned red, it would make a loud buzzing alert, and we were not allowed to speak during the red light.

If you did speak during a red light, you were written a ‘ticket’, and would not be going to recess that afternoon.

It would turn back to green after a specified time.