My school back in the 80s installed a “stoplight” rigged to a decibel meter. If it got too loud it went to yellow then red. When it hit red, it beeped. If it beeped 3 times during lunch, recess was canceled. When it hit yellow, most kids would instantly shut up which reset it back to green.
If I recall lunch policy in total, we had to march to lunch in an alphabetically set line. We were given lunch cards with regular, reduced, or free. You could pay to have money added to the account or pay as needed. Each grade had assigned areas but seating was open. When you were done you could stay inside and talk or go outside after a certain time. Re-entry back to the cafeteria was not allowed.
At a certain time lunch and recess would end and you had to be in line in alphabetical order to go back in to class.