A mobile mosquito alarm, which can only be heard by younger people, is being used at Thatto Heath in St Helens.
Merseyside Police said they had been dealing with an increased number of calls about youth disorder.
But since the device was installed a week ago and police patrols stepped up, complaints have fallen.
'Positive feedback'
The alarm is only audible to those under 25.
Insp Neil Kavanagh, of Merseyside police, said: "It is early days, but it appears to be an effective means of dispersing groups of youths who are causing problems on the streets and distress to local people."
"Since installing the mosquito alarm, not only has the problem been significantly reduced, the local community has also given us positive feedback that the area has greatly improved."
The alarms may be installed across St Helens, if the Thatto Heath device is a continued success.
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