A South Auckland community has installed high-pitch frequency alarms that only young people can hear in a bid to curb vandalism.
Papakura District Council says three of the so-called mosquito alarms, have been installed at Massey Park Stadium and Papakura High School.
They are set to go off after hours in areas that are closed to the public.
They were purchased by the Safer Papakura Trust.
Its chairman Peter Goldsmith says the alarms are set at 17.4 kilohertz, a frequency so high only people aged under 25 can hear it.
Mr Goldsmith says the aim is to drive people away from areas that are popular to graffiti and tag.
Audiologist Leslie Searchfield says the ability to hear high frequencies deteriorates with age.