go to
www.freemosquitoringtones.orgTeens are using high pitched frequencies on their cell phones to alert each other to texts/calls in school. Anyone over the age of 24 can't hear the ringtone.
We actually did an experiment in school today with a 16 year old, me (26), my boss (37) and the other ta (48-50ish).
Everything under 24 years old the teen could hear, but the rest of us couldn't. Once it hit 24 I could almost hear the tone, at 30 and under I could hear it plainly but the older two couldn't. 40 and under my boss could hear it, 60 and under the other coworker did. By the time they got to 60 the teen and I had our hands over our ears because it hurt so much, while the other two could barely hear it.
I just played with it with Dh, and sure enough the first time he heard it was the "39 and under" age group.