New jamming and scanning technology is being rolled out in New South Wales prisons from today to thwart criminals using mobile phones.

The portable body scanners can detect a tiny mobile phone even if it is hidden inside an inmate or visitor.

They will be complemented by signal jamming devices at Lithgow jail, where an initial trial has been extended, and at Goulburn jail for the first time.

Minister for Corrections David Elliott said security had to keep abreast of rapid technological change.

"Mobile phones today can be as small as a 50 cent piece," he said.

"We've had 77,000 searches of visitors to prisons in the last 12 months but unfortunately it's found 320 mobile phones. That has to stop."

The lights on the portable scanner indicate whether or not a phone was detected. ( Supplied: Corrective Services NSW )

The Government plans to roll out the scanners at all maximum and medium security prisons by the end of the year.

The maximum security prison at Lithgow is where convicted killer Bassam Hamzy was being held in 2008 when security cameras captured a mobile phone being passed between cells on a line of dental floss.

Hamzy, who founded the Brothers For Life gang, was ordering brutal kidnappings from inside his cell and making more than 400 calls a day.

In 2009, mobile phones were also found in the cells of gang rapists Bilal and Mohammed Skaf at Goulburn prison.

Corrective Services NSW commissioner Peter Severin said the use of the jamming device in Lithgow was a first for Australia.

"We believe effective jamming technology is the ultimate answer because even if an inmate can smuggle a mobile phone into the prison, it will be worthless," he said.

The State Opposition's Guy Zangari said introducing the scanners was a positive step, but the Government was failing to address the bigger issue of having enough prison officers to supervise the inmates.

"Body scanners can do so much, but of course what the Government really needs to tackle is the fact that through its own budget constraint it has impacted on staffing levels," he said.

"And of course the Government keeps neglecting the fact that we actually have overcrowding in the system."