As you may have gathered, I feel teenagers often get the short end of the stick society-wise. We often allow choices and decision to be made about them that would be considered ageism if applied to any other age group. While I recognize that teenagers are in a space of high growth - physically, mentally and emotionally - we often make rules about and for them that have nothing to do with this. Because, you know, they don't vote. (Whereas - for example - seniors do).
Anyway, in Britain a security group created a tone they call Mosquito (ugh!) that is annoying such that it chases people away. However, since adults have lost the edges of their hearing, it is not audible to adults. They sell this to shopkeepers who are "troubled" by groups of teenagers hanging around their shops. (Apparently the teenagers are not doing anything illegal, or the police would be bought in, so it is simply their continued presence that is being corrected). Now, I'm not really going to go into the fact that these shopkeepers are missing out since teenagers have lots of disposable income (since most don't have utilities and such they are responsible for) or that it would also seemingly affect any of the adult customers with small children who would become unaccountably cranky every time they entered the store.
Because here's what has allegedly happened next. The students turned it into a ringtone. So, since teachers couldn't hear it, the students could receive text messages in class without the teacher knowing. Now, according to Boing Boing, where I found the story, that seems unlikely since the ringtone capabilities do not use the frequencies required to create this sound. But, as pointed out, it really only makes the story better. Because the students have convinced their teachers that they simply can't hear the tones, but that they can.
Update: I stand corrected - apparently with mp3 capability and such on your phone, it is possible to get this sound to work as a tone.