Safe As Milk

Security consultant Howard Stapleton (of Wales) installs security measures for tores frequented by crime. Remembering an childhood episode of discomfort, he discovered a frequency audible to teenagers, but not oldsters like your Safe as Milk crew. He used that frequency to create an annoying chirp to drive away youthful loiterers and shoplifters, and dubbed it The Mosquito (”It’s small and annoying”):

So far, the Mosquito has been road-tested in only one place, at the entrance to the Spar convenience store in this town in South Wales. Like birds perched on telephone wires, surly teenagers used to plant themselves on the railings just outside the door, smoking, drinking, shouting rude words at customers and making regular disruptive forays inside.
…
[The owner] planned to install a sound system that would blast classical music into the parking lot, another method known to horrify hang-out youths into dispersing, but never got around to it. But last month, Stapleton gave him a Mosquito for a free trial. The results were almost instantaneous. It was as if someone had used anti-teenager spray around the entrance, the way you might spray your sofas to keep pets off. Where disaffected youths used to congregate, now there is no one.

From the NYT, via CNET.