A new gadget repels gangs of teenagers by emitting a high-pitched noise that can be heard only by under 20s.
Police are backing the Sonic Teenager Deterrent, nicknamed the Mosquito because of its sound, reports the Daily Telegraph.
It annoys teenagers so intensely they have to clutch their ears. Eventually they can stand it no longer and have to move on.
But because the body's natural ability to detect some frequency wave bands diminishes almost entirely after 20, adults are completely immune.
The £622 black box, which can be attached to the outside wall of shops, offices and homes, sends out 80-decibel bursts of pulsing sounds at up to 16khz.
It sounds to youngsters like a demented insect or a very badly-played violin.
Howard Stapleton, a businessman and former electronics apprentice at British Aerospace, who was sick of youths hanging around outside his shop, came up with the idea.
Working in his bedroom in Merthyr Tydfil, and using his four children as guinea pigs, he came up with a prototype of his device and asked the local shop to test it.
"I got it so that only my kids hated it and my fianceé and I were completely unperturbed," he said. "We put up the prototype outside the store and almost immediately people stopped congregating.
"The beauty of it is that the noise does not have to be loud, just pitched at the right level which affects teenagers."
