Campaigners are calling for a ban on a device that emits a high-pitched sound to disperse groups of teenagers, saying it is not a fair way to treat them.
There are estimated to be 3,500 of the devices, known as the Mosquito, in use in England, many at shopping centres.
Their sound causes discomfort to young ears - but their frequency is above the normal hearing range of people over 25.
England's children's commissioner backs a ban but stores say the devices can be useful against anti-social youths.
What humans can hear
The devices, which exploit the fact that a person's ability to hear high frequencies generally declines once they reach their 20s, have proved popular with councils and police who aim to tackle anti-social behaviour by using them to disperse groups of youths.
But a new campaign called "Buzz off", led by the children's commissioner for England and backed by groups including civil liberties group Liberty, is calling for them to be banned.
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