Interesting story from ABC News about a ringtone that only young people can hear:

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.

While an interesting phenomenon on the aging ear and taking advantage of it - ever hear of "vibrate" mode? Although, some phones vibrate loudly which the teacher can probably pick up.