A while ago, there was a report about a gadget that's supposed to repel teenagers, for example to discourage them from loitering around malls. It does this by emitting a high-pitched sound: one that young people can hear but those above 20 or so typically cannot (since the highest frequency you can hear diminishes as you age).
Now apparently, some teens have used this to their advantage by turning the sound into a ringtone, so they can receive calls and texts in class without their teacher's hearing it.
A sample of the sound, dubbed "Mosquito" or "Teen Buzz", can be found at http://www.bbc.co.uk/wiltshire/audio/mosquito_sound.mp3. See if you can hear it, or whether you just hear the background noise!
I couldn't hear it though my computer's speakers, but I could through headphones -- a kind of high-pitched noise which I couldn't describe further; I'm 31. sonjaaa reports that
An 18-year-old friend described it as an annoying squeal that is loud enough to make her cover her ears. How would you describe it (and how old are you)? And can you usually hear television sets making a similar noise (say, when they're on standby, or when you're far enough away or the volume is turned down far enough that you don't hear the program that's currently playing)?