It all started with "The Mosquito"

The Mosquito Ringtone is a high pitched "Tone" that adults lose the ability to hear as they get older.
The Mosquito is a device invented to annoy teenagers by emitting a very high frequency (17khz - KiloHertz) tone in the hopes that the teenagers will not hang around storefronts. Soon, an Internet craze took over and millions of students learned that they could use the same frequency to their advantage, by using the 17khz or higher tone as their cell phone ringtone, they could receive text messages and phone calls while in class. You see, most adults, usually after age 24, lose the ability to hear high frequency sounds, in fact by the time most people are in their 50s and 60s they might not hear anything higher than a 10khz tone. Hearing aids don't help! And there is nothing you can do, it's a medical condition called Presbycusis.