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DENVER — People living in Denver’s Park Hill neighborhood are on alert because criminals are stealing from their locked cars without any forced entry.

Millions of Americans use a keyless entry fob. It’s a convenient way to lock and unlock a car, but criminals are using a device to grab that signal while keys are inside a home.

On Sunday night, Paul Brown hung his keys by the front door. But when he woke up on Monday morning, he discovered something strange on his home surveillance camera.

“Nobody gets out of the car. But you can see my car unlock — the lights turn on,” Brown said.

A criminal was canvassing his street near Colorado Boulevard and East 23rd Avenue in the Park Hill neighborhood. The surveillance camera captures a car driving up to his 2009 Honda Pilot parked in the street. You can see the headlights flash on and then the suspect is inside – there’s no forced entry, no broken glass.

“I think they were in and out within 30 seconds,” Brown said.

So how was his car unlocked so easily? The FOX31 Problem Solvers talked to a cyber security expert, who said when you unlock your car from a distance, the key fob sends an electronic code to your vehicle. Thieves now purchase a device to steal that code if the fob is at close-range.

“These detectors they’re using have a range of up to 300 feet – so that’s like a football field away. It’s pretty far,” said Ray Hutchins, managing partner at CyberCecurity LLC. “If they’re targeting you, they can see when your fob is talking to the car.”

Luckily, Brown didn’t have anything valuable inside his car. But he wants others to be careful about where they hang up their keys.

“People need to be aware there’s an easy way to break into your car,” he said.

Hutchins recommends keeping your key fob at a safe distance if possible. You could also buy a “fob guard security pouch.” It’s made of metal to block the hacker.

“The only way to truly solve this is at the car manufacturing level and the insurance company level. They’ve got to cooperate to defeat this in the engineering of the products. Right now, they are insecure,” Hutchins said.