If you're an adult who feels disadvantaged over the fact that teenagers know more than you about technology, here's a story to make you feel over-the-hill.
It turns out, teenagers are now downloading a ring tone for their phones for incoming calls and text messages that is pitched too high for most adults to hear. If you've ever been near one of those devices that people install in their gardens to keeps critters from digging, you'll know that most adults over 30 cannot perceive the sound due to age-related hearing degradation, but most young people in their teens and early to mid 20s can hear acutely, even painfully. Some shopping malls today even project the sound in places they don't want teen mall rats to congregate.
It seems the young people have found a way to use the sound to their advantage to hear when text messages come in during class.