British shopkeepers have a new tool to discourage loitering teenagers:

Shopkeepers in central England have been trying out a new device that emits an uncomfortable high-pitched noise designed to disperse young loiterers outside their stores without bothering adults. [...]

"The noise can normally only be heard by those between 12 and 22 and it makes the listener feel uncomfortable," she added.

Here in Virginia, I can remember a local 7-11 employing a similar strategy, using classical music.