For classrooms where cellphone use is forbidden, students have found a ring tone that many adults cannot hear.
"The cellphone ring tone [... is] 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."
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