The ringtone, known as 'Teen Buzz' or 'Mozzy Tone', emits an ultra highpitched sound that most people over 20 cannot hear, and is being used by teenagers around the world to trick their teachers and parents.

The principle behind the technology is a biological reality that hearing experts refer to as presbycusis, or 'aging ear'.

The ringtone was originally developed by the UK-based company, Compound Security Systems Ltd, as a 'teenage repellent' that could be used by business owners to stop youngsters gathering in groups outside their premises, while leaving adults unaffected.

However, according to Simon Morris, marketing director of the company, someone who could obviously hear the sound decided to reinvent it as a ringtone, and turn the advantage back to teenagers. "You've got to give the kids credit for their ingenuity, " he said.

Morris said the company received so much attention on foot of the pirated ringtone that they decided to develop their own version of the product.

It is called Mosquitotone, and Morris hopes it will soon be available to download via the internet all over the world.

While Compound Security Systems have no figures yet to indicate how well the ringtone is selling, Morris believes it will be good news for the company.

"We've had four million hits on our website since we launched it, so I can only assume it's going well, " he said.