A ringtone which prying elders can't hear -- if you think it is just a teen fantasy, step aside.
Cellphones, which youngsters can hear but most adults can't, are now in vogue in American schools.
The technology is based on the fact that most adults gradually lose the ability to hear high pitched sounds and was developed in Britain.
But recently, it has spread to the US where schools are banning students from bringing cell phones to class rooms.
The use of peculiar ring tones came to light recently in a school in New York where the cell phones must be turned off in class rooms, New York Times reported.
The Times said last week, a high pitched ring tone went off that set teeth on edge including their 28-year old teacher.
When she asked whose cell phone it was, the students were surprised and asked her how could she hear it when it should be inaudible to adults. But apparently her ears had not yet lost the sensitivity.
The Times says that cell phone ring tone was the offshoot of an invention called the Mosquito, developed last year by a Welsh security company to annoy teenagers and gratify adults, not the other way around.
It was marketed as an ultrasonic teenager repellent, an ear-splitting 17-kilohertz buzzer designed to help shopkeepers disperse young people loitering in front of their stores while leaving adults unaffected.
The principle behind it, says the report, is a biological reality that hearing experts refer to as presbycusis, or aging ear. Most adults over 40 or 50 seem to have some symptoms, scientists say.
While most human communication takes place in a frequency range between 200 and 8,000 hertz, (a hertz being the scientific unit of frequency equal to one cycle per second) most adults' ability to hear frequencies higher than that begins to deteriorate in early middle age.
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