I was visiting the University of Florida campus recently (great place) and noticed a lack of sirens, which have become commonplace on most campuses. I checked out their emergency preparedness plan and found that they have a device called LRAD 500. Here is a link:
http://www.atcsd.com/site/content/view/205/110/
Apparently, it is mounted on a truck and can be directed at a section of campus. They only have one, however, which seems odd since its a large campus. Anyone seen this in action??