The Mosquito emits a high-pitched noise in an audio range lost by most people by their 20s.
Rochdale fitted it at a nursing home after complaints about teenagers loitering outside the building.
Community safety officer Lee Durrant said: 'The area is an antisocial behaviour hot-spot.
Mr Durrant admitted the device would move teenagers elsewhere, and said the council had organised activities to try to keep them off the streets.
But Kathy Evans, policy director of the Children's Society, said the device's use 'sent out a horrible message to young people about how their community sees them'.
She predicted a legal challenge because the device affects any young person nearby, whether or not they are misbehaving.
George McNamara, policy officer at the NCH charity, said: 'This indiscriminately targets young people, when adults cause as much anti-social behaviour through being drunk and disorderly.'