From Guardian Unlimited Technology…

A friend has two children aged 11 and 16. He explains: “The latest thing in Surrey right now is downloading high-pitched tones that only children can hear [the 17kHz “Mosquito”] on to their mobiles, Bluetoothing them around, and then starting up a cacophony in lessons – they can hear it and double up in agony, but their teacher can’t.” It’s a metaphor for the adult/child gap: the children can recognise what the grownups can’t.