Corrections has quietly removed all cellphone jammers from prisons.

The technology, introduced in 2008-09 to prevent inmates using smuggled mobile phones, has cost more than $17 million.

But signal blocker have not been in use since June after being found to interfere with new prison guard safety systems.

When announcing their introduction, then Corrections Minister Phil Goff said cellphone blocking in New Zealand prisons was a major step forward that will stop prisoners committing further offences while behind bars.

Stuff recently obtained details under the Official Information Act about the number of cellphones seized from the 18 prisons run by Corrections over the past three years.

There were 626 cellphones and more than 750 cellphone-related items (such as batteries, chargers, SIM cards etc) found by Corrections staff between January 2023 and November this year.

When asked why inmates would be smuggling cellphones when the prisons had the mobile signal jammer that should render them useless, Corrections chief custodial officer Neil Beales said the cellphone jammers were removed in June.

The jammers had been found to interfere with new safety systems such as Corrections officer safety alarms, he said.

Advances in cellular technology had also resulted in jammers becoming increasingly obsolete.

It was only one of a number of tools used to stop cellphones being used in prisons and a number of more effective tools remain in place, Beales said.

These include Cellsense devices, which detect a range of metals found in cellphones, alongside screening and x-ray capability as well as detection dogs.

Some people in prison go to extreme and elaborate lengths to introduce contraband into prisons, and we are constantly working to stay one step ahead of new methods used to introduce contraband into our prisons, Beale said.

Corrections was looking at new and emerging technology to complement systems already in place, he said, and had started introducing the use of full body imaging technology at a number of sites to detect contraband that has been concealed on or in a persons body.

In 2018 Corrections admitted cellphone jamming technology created a communications blind spot near Rimutaka Prison, meaning residents of a child sex offender unit outside the wire could not be tracked on-site at the facility.

Cellphones could be used by inmates to put pressure on others outside the wire, or to co-ordinate drug deals, and other offending. In May this year nine prison staff at Rimutaka were suspended for alleged misconduct, including the smuggling of cellphones into the prison.

Drug and alcohol counsellor and criminologist Roger Brooking, who has been critical of the spending on jammers from the outset, said it was not surprising that Corrections had ditched the technology.

They dont work. They never have worked, he said.

What prisoners have told me is that they have always managed to find areas within the prisons where the jammer just doesnt seem to operate. So prisoners have been able to continue making cellphone calls to conduct drug deals, talk to family or whatever.