Authorities plan electronic monitoring of up to 200 high-risk released prisoners.
Twenty-five high-risk sex offenders are now being tracked around the clock, with the Corrections Department planning to dramatically expand its GPS monitoring scheme to 200 ex-prisoners this year.
As many as 50 offenders were wearing GPS ankle bracelets by the end of last year as the Government stepped up its drive to monitor convicted offenders in the community. Nearly half of the offenders being watched were living in communities in the lower North Island.
The department revealed the programme, which cost $750,000 a year, had detected two breaches since it was rolled out in August.
Corrections Minister Anne Tolley said these breaches confirmed the value of the GPS scheme.
"If they say they are going to visit someone in a hospice but actually they're a block away in a McDonald's where there are kids, and they're not meant to be near kids, we now know that. Whereas before when they report in or when we have a visit to their house, they're telling us that that's what they've done, now we can actually see."
Before the technology was introduced, offenders had to check in to police stations or get approval to make supervised outings.
Now that the ankle bracelets can be produced cheaply and charged easily, judges or the Parole Board can request that high-risk offenders be fitted with GPS locators as a condition of their release.
The GPS devices send out a signal every minute. If the offender strays into "exclusion zones" - schools, parks or near victims - or breaks their curfew an alarm sounds at the Corrections Department offices in Wellington.
Officials call police in that region immediately, or on some occasions ring the offender directly to warn them to leave the area. It is understood convicted rapist Stewart Murray Wilson, now living in Wanganui, was given a mobile phone by Corrections when he was released from jail, in part because it meant he could be called immediately if he went into exclusion zones.
Offenders with GPS locators have to charge their own ankle bracelet, and if the charge becomes low Corrections or police will be called to investigate.
The new technology is part of a series of policy changes designed to reduce reoffending by 25 per cent within five years.
Justice Minister Judith Collins introduced legislation last September which would give authorities power to recall dangerous ex-prisoners to jail indefinitely. The "public protection orders" will be debated in Parliament this year.
Corrections is also developing a register which would allow violent or sexual offenders to be monitored for the rest of their lives.
Mrs Tolley said the register would be the main piece of Corrections policy to be developed in 2013.
It would be based on a British scheme in which offenders were risk-assessed when released and their address, jobs and relationships were closely monitored. Ex-inmates were required to check in with authorities at least once a year.
Keeping close watch
Offenders with GPS locators
Northern North Island - 7
Central North Island - 3
Lower North Island - 9
South Island - 6.