Teacher-proof high-pitched ring tone latest buzz in US classrooms

A high-pitched sound developed in Britain to deter teen loitering and inaudible to most adults has invaded US classrooms where youngsters are using it in their cell phones to communicate without their teacher's knowledge.

The ring-tone, know as "Teen Buzz," allows students to surreptitiously exchange text messages unbeknownst to teachers whose older ears cannot detect the sound.

A security company in Wales developed the tone -- the Mosquito Teen Repeller -- to drive away teens loitering around shopping malls in Britain,

But US teens have created their own version of the piercing sound and are selling it on the Internet for 2.99 dollars.

Most adults are unable to hear the tone as with age people are less likely to hear high-frequency sounds.

At 17,000 Hertz, Teen Buzz falls within the highest of pitches noticeable to humans, who can hear as low as 40-50 Hz and as high as 20,000 Hz.

"Because the range of hearing varies greatly in individuals, it is possible that the teachers who do not hear this ring tone have never been able to hear up to the 17,000 range," said Stanton Jones, an audiologist at the St. Louis University School of Medicine. "Or age-related hearing loss may make the tone undetectable."

Children can hear high pitches. "Age-related hearing loss, or presbycusis, begins around age 35 with the highest pitches being lost first," Jones said.