WA Police have been forced to abandon technology used to detect unlicensed vehicles because they cannot cope with the huge number of alerts, Police Commissioner Karl O'Callaghan has revealed.

In 2009, the State Government scrapped car registration stickers in favour of a computer system, which scans number plates and automatically provides officers with an instant alert if a car's registration has expired.

At the time it was heralded as cutting-edge technology that would save the Government millions of dollars.

But Commissioner O'Callaghan has told a budget estimates hearing police have been forced to turn off part of the system so they can focus on other alerts, such as those notifying officers that a child sex offender is in a restricted area.

"With the advanced traffic management vehicles, we've turned off that unlicensed alert because of the high number of alerts we get that we can't cope with," he said.

"These things could just be one day out of licence, so they're still within their renewable period."

Commissioner O'Callaghan told the hearing the system has become a headache for police, because it cannot differentiate between a vehicle that has been unlicensed for a time within the grace period, or for several months.

System failure sparks insurance, safety fears

The State Opposition's Transport spokesman, Ken Travers, said the admission was proof the Government should never have scrapped car registration stickers.

"The Government has clearly given up, and it shows that we are seeing more unlicensed vehicles on our roads, because of a bad decision taken by the Barnett Government some four years ago," he said.

Mr Travers said it would now be difficult for police to immediately detect whether a car was not registered.

"They can't now, unless they manually enter in the licence plate of the vehicle," he said.

"Previously they could have looked over, seen a sticker, realised that car was clearly licensed and moved on, now they'll have to go in and manually do it.

"That's very time consuming, what I think it's going to see is an increase in unlicensed vehicles on our roads.

"That has real impacts in terms of third party insurance for the broader community."

A spokesman for Police Minister Liza Harvey said the technology was being used to target high-end criminal activity, repeat drink-driving offenders and motorists without a driver's licence.