Can I hear what?

A recent product development in the US, to stop kids hanging around malls, was to play a high pitched noise at the store entrance.  As we get older, our ability to hear higher frequencies deteriorates, and only kids can hear this noise (apparently, ‘coz I can’t hear it but that doesn’t mean it’s actually there!).

Now, enterprising kids are using this sound as ringtones on their ‘phones so that they can get calls in class, knowing that the teacher won’t be able to hear the ring.

Check it out for yourselves here and see if you can hear a high-pitched cricket-type of chirping.  Now, if can only get those crickets to say “Clean your room…clean your room”…