Mosquito, the controversial device designed to break up groups of troublesome teenagers, has been redesigned to annoy people of all ages.

The original Mosquito device, which emitted a high-pitched noise audible only to under-20s, had been criticised by human rights campaigners for discriminating against young people.

With this in mind, the new Mark 4 version operates at a much lower frequency that adults can hear too, annoying everyone within earshot.

Mosquito manufacturer Compound Security Systems is confident that the new device will be well-received by retailers and police.

"It's something we've been asked for by a lot of law enforcement agencies in Britain and abroad," said commercial director Simon Morris.

The company is expecting demand for the new Mark 4 Mosquito to soar as the credit crisis worsens.

"The less money people have, the more likely they are to start going out and causing trouble," Morris said. "Usually, when the economy turns down the security industry picks up."