From New York Times

In that old battle of the wills between young people and their keepers, the young have found a new weapon that could change the balance of power on the cellphone front: a ring tone that many adults cannot hear.

In settings where cellphone use is forbidden — in class, for example — it is perfect for signaling the arrival of a text message without being detected by an elder of the species.

“When I heard about it I didn’t believe it at first,” said Donna Lewis, a technology teacher at the Trinity School in Manhattan. “But one of the kids gave me a copy, and I sent it to a colleague. She played it for her first graders. All of them could hear it, and neither she nor I could.”

The technology, which relies on the fact that most adults gradually lose the ability to hear high-pitched sounds, was developed in Britain but has only recently spread to America — by Internet, of course.

…..

The cellphone ring tone that she heard 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 is a biological reality that hearing experts refer to as presbycusis, or aging ear. While Miss Musorofiti is not likely to have it, 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.

Thanks to AgentWiggles for sending in the “official” file. You can download it here

Want to generate your own tones??… download and open Audacity…

Generate > Tone

Waveform: Sine
Frequency: 18000.00
Amplitude: 1.00

*generate tone*
MP3 File <–Wtf I can’t hear anything! (I guess I am old)