For years the hooded youths of Britain have been free to roam the country’s shopping streets. In the evenings and at the weekends they have loitered outside the shops of their choice.

But that is all beginning to change, and no thanks to ASBOs. Across the nation a mysterious high-pitched whine has been driving the youngsters from their natural habitats outside supermarkets, stations and leisure centres.

The source of the sound is a high-frequency ultrasonic device called the Mosquito that is inaudible to anyone aged over 25 but intolerable to anyone under that age.

More than 3,000 Mosquitos have been sold since they went on the market last year and they are being used by a growing number of police forces, shops, train companies, banks and local authorities to move on troublesome groups of youths. The devices cost £495, have a range of 15 to 20 metres and are harmless, according to the manufacturer, Compound Security Systems.

Co-op and Spar have ordered about 100 each, the manufacturers say. Sainsbury and McDonald’s have a dozen, Aldi at least nine, Tesco a couple, and Waitrose two.

Simon Morris, commercial director of Compound Security, said: “As soon as the Mosquito goes in, theft goes down, trade increases and profits go up. One of the Co-ops said their trade went up £3,000 in the first week. They were amazed by it. If there are no kids hanging around, people feel more comfortable going into the shop and hence spend more money.”

Marks & Spencer has a device on trial outside its latest Simply Food shop in Blackheath, southeast London on the recommendation of the police.

An M&S spokeswoman said that the Mosquito was perfectly safe and completely legal. “It is definitely only a trial for that store, not a national roll-out,” she said. No decision had yet been made on whether to keep the device, she said.

The Mosquito is supplied with a warning sign to alert people to the presence of the device, but no sign was in evidence outside Simply Food in Blackheath Standard when The Times visited yesterday. Sophie O’Dowd, 14, who lives locally, noticed a strange noise while she waited outside the shop for a friend after school. She said: “It is like a constant buzzing. It is really annoying and you just want to move away from it.”

Her mother, Suzanne O’Dowd, was annoyed that M&S is testing the device without giving any warning. “I do not agree with it at all,” she said. “I want to know how it affects babies and children: is there any risk? There should be some sort of warning.”

Arriva trains, Northern Rail and Chiltern Railways have also invested in the technology. At least eight police forces, including the Metropolitan Police, have been supplied with the device, and JNE Marketing, which distributes the Mosquito, said that it had supplied councils across the country.

Ken Povey, the company’s managing director, said: “Lots of schools and colleges are now using the unit too.”

Sainsbury confirmed that it was testing about a dozen of the devices in a handful of shops around the country.

Sound bites

— The Mosquito, right, automatically adjusts its volume so that it is only five decibels above local noise levels, an increase equivalent to a whisper

— The device, which went on the market in January last year and modified in August, now has an inbuilt cut-off after 20 minutes’ use

— Its average volume level is 85 decibels, the same as the dialling tone on an average telephone, and far less than playing the violin (120 decibels) or an iPod (104 decibels at volume level 5)

— The manufacturer, claims that 90 per cent of people aged over 25 cannot hear the device because of natural age-related hearing loss

— This week the company, which is based in Merthyr Tydfil, brought out a new model, the GSM Mosquito, which can be turned on and off simply by sending a text message to the device by mobile phone

Source: Compound Security Systems

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