CBS News Correspondent Richard Roth
Dubbed "The Mosquito" by inventor Howard Stapleton, the machine looks like a box with a small loudspeaker attached, and is mounted over the store's entrance.
Roth did a quick survey of some teens at the store.
One said he could hear the noise, then scampered away.
Another said is sounded like a repetitive "deep, deep, deep" and was indeed grating.
Yet another described it as resembling "a violin string (being rubbed), but really, really, really high pitched."
The sound, Roth explains, is supposed to work as a repellant for a simple reason: Most people over 30 can't hear it, most people under 20 can, and hate it.
Roth chatted with Stapleton, who modified the sound for him so older people, including Roth, could pick it up.
Normally, the device is tuned to emit a pulsing high-frequency tone, inaudible to most aging ears and deeply annoying to younger ones.
"It's relatively small; it's very annoying. That sounds like a mosquito to me," Stapleton told Roth, in explaining why he named it "The Mosquito."
He used his own kids as guinea pigs.
Roth says Stapleton is dreaming of a swarm of mosquitoes throughout Britain, wherever teen-age loiterers are perceived as a problem, to coax them to leave.
"Once it gets in your head," Stapleton says, "it's very difficult to shake off, and the only way to shake it off is to move away."
Over eight weeks of testing, that's exactly what's happened at the Welsh convenience store.
"They've gone straightaway, like, you know, so we don't have them hanging around like we used to," a woman behind the counter says.
Apparently, Roth adds, only the 'hanging-around' crowd finds the sound annoying: It doesn't seem to bother dogs, and customers who keep moving hardly notice it.