A youth advocate says high-pitch frequency alarms that only young people can hear could unfairly discriminate against them.
The so-called Mosquito alarms are set at 17.4 kilohertz, a frequency so high only people aged under 25 can hear it.
The Safer Papakura Trust has installed them at two locations in Papakura, south of Auckland, in an effort to stop taggers and vandals destroying property in the area.
They are switched on at at Massey Park Stadium and Papakura High School at hours when no-one should be there.
But the senior solicitor at the Youth Law Institute, John Hancock, says he has concerns about the alarms being used to deter young people using public spaces.
Mr Hancock says while using the alarm on private property is not an issue, a device that solely targets a certain group of people could be also be seen as a discriminatory act.