By ASHLEE MULLANY
GPS devices that are supposed to track our worst child-sex predators lose their signal inside big buildings - including shopping centres.
The State Government has admitted the devices, which were recently fitted to 18 offenders, have "building mass limitations".
"They work like mobile phones so there may be black spots," a Corrective Services spokesman said.
"Some shopping centres may be affected."
This is despite a shopping centre being the scene of one of the state's most shocking child-sex crimes when Sofia Rodriguez-Urrutia-Shu, 8, was raped and killed inside a centre toilet in Canning Vale.
The Sunday Times can reveal the technology is so limited that one of the 18 offenders fitted with them contacted the newspaper this week to say he constantly "goes off the grid".
The dangerous sex offender claimed he was phoned several times last week because authorities could not pick up his location.
He said the device had blacked out in underground carparks, shopping centres, regional areas and even in his own home.
He sent a picture showing his signal had been lost inside a shopping centre.
The offender said he was speaking out because he believed the devices were ineffective and no deterrent.
"I've cleaned up my act and I've done enough jail time to know I don't want to go back," he said. "But they're lying to the general public when they say these things work. It's a joke." A Corrective Services spokesman said the department carried out tests on the devices before they were rolled out and found "some places had better coverage than others".
"It's another tool in our arsenal for monitoring dangerous sex offenders," he said.
The Barnett Government has previously said the GPS tracking devices would be a vital tool to monitor sex offenders.
But in April, The Sunday Times revealed the company awarded the $750,000 contract to provide the ankle bracelets had been dumped in California for producing devices "inundated with defects".
The Corrective Services spokesman said they were working to "address issues" with the new bracelets.
"When an alert is received that there is no GPS signal an automated message is sent to the offender to go outside to enable the system to re-establish GPS connection," he said.