AT least three York convenience stores are now using hi-tech sonic devices to drive unwanted gangs away from their premises, The Press has learned.

We revealed last week the Co-op shop in Tang Hall Lane had fitted a mosquito device, which keeps youngsters away by emitting an piercing, high-frequency noise, audible only to people under 25.

Spar said it was also using the devices at its branches in Lowther Street, The Groves, and Huntington Road.

A spokesperson said: "Since installing these, Spar can confirm it has helped combat problems of youths loitering. Spar is committed to providing a welcoming and unintimidating environment for its customers."

Tom Metcalfe, manager of the Lowther Street store, said: "The trouble has died down a lot since we had it installed. It's a combination of that and more male staff."

The device uses a medical phenomenon called presbycusis - age-related hearing loss - which sees people lose their ability to hear sounds in the highest range, from the age of about 20.

Mr Metcalfe said: "If there are bunches of lads outside, it does annoy them.

"There were a lot of idiots hanging round causing trouble, nicking beer and pulling the shutters down. It's a lot better now."

A staff member at the Huntington Road branch said: "We needed it. We had trouble with young people gathering in front of the shop. We have had it a few months and it has worked. Soon after we got it, we also had police helping us more."