NEW YORK (CBSNewYork) — The number of stolen cars has been cut in half over the past 20 years, as technology improved.

Now, some criminals are using technology to get inside modern-day vehicles — which might explain a small spike in thefts.

As CBS2’s Chris Martinez explained, authorities have seen an increasing number of break-ins that involve suspects getting into vehicles without visible tools.

Two-years-ago, Michael Shin said he captured footage of a man opening his car and holding a backpack. No break-in tools were required, and Shin said he always locked his car.

“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 and start their cars with the push of a button.

“You can’t stop this kind of theft right now,” explained Roger Morris, Chief Communications Officer at the National Insurance Crime Bureau.

Morris said two devices can be used to mimic a key fob. In a recreation, a man gets out of his car and uses the fob to lock it. Morris then used a relay box to intercept the fob’s code. The code is then sent to a second man with a small box that acts as the vehicle’s fob allowing him to unlock the car, open the door, and drive away.

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

The boxes came 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 care is basically a computer on wheels and if they can hack into that system and defeat it,” Morris said.

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

The National Insurance Crime Lab said 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.