Alarm when your library is too loud?

Boisterous talk over at the Chronicle Wired Campus this morning about the potential of an alarm/flashing lights in academic libraries when the decibel level gets too loud.

To me, this seems like overkill. But then again I wouldn't want to go around shushing any more than anyone else. So maybe you can establish the top floor/West wing, etc. as the group study/open talk area...and the rest of the building can be a quieter zone?

An alarm would seem more obtrusive, to me. But I do remember well from my student days, the intercom to tell us that the library was closing in 15 minutes. Could you simply use it?