Today's New York Times profiles an invention that emits a high-frequency sound designed to annoy people younger than 20. Apparently, people older than 30 can't hear it. Howard Stapleton of Barry, Wales invented the device, called the Mosquito, to drive away teenagers loitering around storefronts. From the NYT:
A trip to Spar here in Barry confirmed the strange truth of the phenomenon. The Mosquito is positioned just outside the door. Although this reporter could not hear anything, being too old, several young people attested to the fact that yes, there was a noise, and yes, it was extremely annoying.
"It's loud and squeaky and it just goes through you," said Jodie Evans, 15, who was shopping at the store even though she was supposed to be in school. "It gets inside you…"
Stapleton, a security consultant whose experience in installing store alarms and the like alerted him to the gravity of the loitering problem, studied other teenage-repellents as part of his research. Some shops, for example, use "zit lamps," which drive teenagers away by casting a blue light onto their spotty skin, accentuating any whiteheads and other blemishes.
Using his children as guinea pigs, he tried a number of different noise and frequency levels, testing a single-toned unit before settling on a pulsating tone which, he said, is more unbearable, and which can be broadcast at 75 decibels, within government auditory-safety limits. "I didn't want to make it hurt," Stapleton said. "It just has to nag at them."