The device, called the Mosquito ("It's small and annoying," Mr. Stapleton said), emits a high-frequency pulsing sound that, he says, can be heard by most people younger than 20 and almost no one older than 30. The sound is designed to so irritate young people that after several minutes, they cannot stand it and go away.
At first, members of the usual crowd tried to gather as normal, repeatedly going inside the store with their fingers in their ears and "begging me to turn it off," Mr. Gough said. But he held firm and neatly avoided possible aggressive confrontations: "I told them it was to keep birds away because of the bird flu epidemic."The problem is that it's only most, not all, people over 30 who are immune to its effects.
Andrew King, a professor of neurophysiology at Oxford University, said in an e-mail interview that while the ability to hear high frequencies deteriorates with age, the change happens so gradually that many non-teenagers might well hear the Mosquito's noise. "Unless the store owners wish to sell their goods only to senior citizens," he wrote, "I doubt that this would work."The article describes other devices for keeping the young and disorderly at bay, including "zit lamps", which cast a blue light that accentuates acne, and the old standby, classical music.
IANAL, but I wonder if the "Mosquito" device could possibly be considered a statutory nuisance in England & Wales under s79(1)(g) "noise emitted from premises so as to be prejudicial to health or a nuisance" of the Environmental Protection Act 1990? If it inconveniences someone who isn't a "hoodie wearing yob", perhaps they might convince the local authority to serve a s80 abatement notice, with a GBP20k max fine for non-compliance. The act is at http://www.opsi.gov.uk/acts/acts1990/Ukpga_19900043_en_4.htm#mdiv79
I quite like the "zit lamps" and classical music ideas, though - those don't seem to cross the line into vigilante collective punishment territory.
and by my reckoning, loud music and graffiti are over 30s repellent...lol