Some students are downloading a ring tone off the Internet that is too high-pitched to be heard by most adults. With it, high schoolers can receive text message alerts on their cell phones without the teacher knowing.

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NEW YORK (AP) - Students are using a new ring tone to receive messages in class -- and many teachers can't even hear the ring.

Some students are downloading a ring tone off the Internet that is too high-pitched to be heard by most adults. With it, high schoolers can receive text message alerts on their cell phones without the teacher knowing.

As people age, many develop what's known as aging ear -- a loss of the ability to hear higher-frequency sounds.

The ring tone is a spin-off of technology that was originally meant to repel teenagers -- not help them. A Welsh security company developed the tone to help shopkeepers disperse young people loitering in front of their stores while leaving adults unaffected. The company called their product the "Mosquito."

Donna Lewis, a teacher in Manhattan, says her colleague played the ring for a classroom of first-graders -- and all of them could hear it, while the adults couldn't hear anything.