What Are You Deaf, Gramps?

Students are turning to special children-only ringtones to evade hard-of-hearing teachers:

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.

. . .

The cellphone 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 is a biological reality that hearing experts refer to as presbycusis, or aging ear . . . [and] 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.

“It’s the most common sensory abnormality in the world,” said Dr. Rick A. Friedman, an ear surgeon and research scientist at the House Ear Institute in Los Angeles.

But in a bit of techno-jujitsu, someone — a person unknown at this time, but probably not someone with presbycusis — realized that the Mosquito, which uses this common adult abnormality to adults’ advantage, could be turned against them.

The Mosquito noise was reinvented as a ring tone.