Device for high-frequency sounds to prevent loitering by teenagers

This device is not without controversy:

http://www.bbc.co.uk/news/10412057

http://en.wikipedia.org/wiki/The_Mosquito#Opposition

http://en.wikipedia.org/wiki/The_Mosquito#Legal_status

http://www.liberty-human-rights.org.uk/issues/young-peoples-...

http://www.dailymail.co.uk/news/article-513822/Buzz-Outcry-C...

I enjoyed scrolling to the bottom to listen to the different sounds the device can produce. The disclosed age/frequency pairs seem remarkably accurate and, of course, the sound is quite annoying.

My local library solved this problem by blasting three different operas at obnoxious levels just outside the doorways.

It works, but it makes me cringe every time I walk into the library.