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GPS helped change our perception of crime.

In movies, following the bad guys on foot or by car was always fraught with danger and the sudden interference of a random slow pedestrian or Volvo driver.

Subsequently, the sudden ability to slip a GPS tracker on the bad guys' car meant the police could munch on donuts and cheerily wait for their prey to stop when nature called.

It seems, though, that in the heart of movieland, technology is messing with the script.

As the LA Times reported Thursday, GPS trackers that are being placed on serious criminals released on probation aren't always proving themselves effective.

Indeed, in a six-week period earlier this year, one in four malfunctioned. Which meant that hardened types wandered around LA with solid abandon.

These figures were tracked down in a probation department audit that makes for quite dramatic reading. Two more eye-opening data points from the audit, which covered the period between August 1 and September 11:

51 out of 196 released criminals had to exchange their GPS monitors because, for some reason, they didn't work.

1 released felon had to exchange his monitor as many as 11 times.

You'll be wondering about the faults experienced by these supposedly infallible machines. There were reportedly low batteries, batteries that simply wouldn't charge enough, and devices that kept offering an alarm signal for no reason.

In one case, the monitors lost track of a criminal for five days.

Sentinel, the company responsible for maintaining the trackers, replied to the audit in great detail. It suggested, in part, that probation officers needed more training and that felons don't always follow the charging instructions. The company also insisted that it had worked with the LA County Probation Department for 21 years and took these issues very seriously.

Clearly, Sentinel believes there have been communication problems between it and the probation department.

However, because of cost savings, it's inevitable that greater reliance will be placed on technology to monitor offenders who might be released back into the free world. These are serious offenders who have served time for domestic violence, sex offenses, and gang violence.

If as many as 25 percent of them go suddenly AWOL, it might cause an additional ripple of insecurity in an already troubled world.