A DEVICE outside a Newport shop is helping disperse gangs of anti-social yobs peacefully.

For years the Spar shop in Caerleon Road was plagued by youths who hung around outside smoking, drinking, hurling abuse at customers and throwing crates at passing cars.

But now the louts are taking flight - thanks to a new 'Mosquito' device only tested at a handful of shops in the UK.

The black box device, fixed to an outside wall by police, emits a high-frequency pulsing sound that can be heard by most people younger than 20 and almost nobody older than 30.

It is designed so to irritate young people that after several minutes they cannot stand it and go away.

Spar shop manager Sue Oates, 54, hailed it a success as instead of phoning the police three times a week, staff had not dialled 999 for over a month.

"Around 20 teenagers aged 16-plus would often hang around outside the shop creating a lot of noise," she said. "Customers felt intimidated when they came down in the evening. It was very frightening for them and had a knock-on effect on trade.

"But since the Mosquito has been there the number of youths has dropped dramatically so staff and customers feel a lot safer."

Mrs Oates said six of her staff, who were under the age of 21, could hear the noise.

"They say it's a very high pitched noise that is quite irritating when they are outside the shop," she said.

Installed about two months ago, Mrs Oates is hoping the device will continue to keep gangs away. "It has been very successful," she said.

"But it is still the winter so there are not as many kids hanging about outside. We'll have to wait and see how effective it is in the summer."

Andrew Beese, 20, who works part time in the shop, described the Mosquito sound as "uncomfortable" and "irritating".

"It's what you'd expect a dog whistle to sound like - a really high-pitched whine.

"I wouldn't want to sit round that noise constantly, it's not something you can just ignore."

More than 100 stores and some councils have placed orders for the device, which was invented by Howard Stapleton, of Merthyr Tydfil.

He came up with the idea after reading how hearing levels changed with age.

It costs about £500, and the noise cannot be heard inside the shop.

A Gwent Police Authority report praised the effect it had had in Caerleon Road, and said it would recommend the device for use in other areas of Gwent.