There is a very annoying tone similar to a buzzing mosquito that can generally only be heard by people under the age of 25. It's sometimes played in malls and shops as a repellent against loitering teenagers. Ya' know, those hooligans. Of course in the ever escalating battle between kids and authority figures ("The Man"), some students adopted that same sound as a ring tone or alert for their cell phone that teachers ("Old Fogies") can't hear.
Try the "Teenager Audio Test" to check whether you can hear the sound.
I could. You?
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