From the Chronicle of Higher Education:
To tamp down the noise level in their libraries, some colleges are considering installing a warning system that looks like a traffic signal. Called the Deluxe Yacker Tracker, the device flashes a yellow light to indicate when the noise exceeds a certain level. When it exceeds the level by at least 15 decibels, the red light illuminates and a siren can go off, too.
As the author of this little snippet comments,
What ever happened to just approaching students and telling them to keep it down?—-Andrea L. Foster