Does it? I much prefer an objective measure of volume instead of a school staff member just writing individual kids up for being subjectively too loud---the machine should have much less bias.
Why do they need to be quiet? This is in a cafeteria, not in a classroom.
I remember the elementary and middle school cafeterias being host to an occasional screaming match, so I can see why they would want to keep it at a reasonable volume. It might be a little over the top to have the traffic light thing, but it's better than the subjective alternative.