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MIAMI (CBSMiami) – The number of stolen cars has dropped in half over the past 20 years as technology improved.

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But now some criminals are using technology to get into modern-day vehicles.

Authorities are seeing an increasing number of break-ins.

In one case caught on camera, two men get into two cars with ease – holding nothing but a small box in their hands.

Two years ago, CBS News spoke with Michael Shin.

He captured footage of a man holding a backpack opening his car with no break-in tools needed.

Shin says he always locked it.

“It’s just a little unnerving that they could so easily just walk into my car and pretty much without any recourse without anybody really noticing,” Shin said.

For years, police didn’t know how thieves were doing it.

But now insurance investigators believe criminals are taking advantage of modern key fobs that allow owners to unlock their car and start it with the push of a button.

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“You can’t stop this kind of theft right now,” said Roger Morris.

Morris, who’s the chief communications officer with the National Insurance Crime Bureau, says two devices can be used to mimic a key fob.

According to Morris, thieves wait nearby for someone to lock their car using a fob.

As the car is being electronically locked, the criminals use a relay box to intercept the fob’s code.

The code is then immediately sent to a second man with a small box that now acts as the vehicle’s fob – allowing him to unlock the car, open the door, start the car and drive away.

“We tested 35 vehicles… 18 of them we were able to start with the device as well and drive off,” Morris said.

The boxes come from a company that works with law enforcement, but Morris believes professional criminals have figured out how to make their own.

They can be used to take a vehicle immediately or crooks can save the code and steal the car later on.

“Today’s cars is basically a computer on wheels and if they can hack into that system and defeat it,” Morris said.

These devices may explain a recent increase in car thefts and law enforcement have yet to figure out how to stop it.

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The National Insurance Crime Lab says drivers who own vehicles with this technology should be careful when they lock their vehicles and look for anyone near them acting suspiciously or carrying a strange device.