SAN ANTONIO — As cars become more high-tech, thieves are using new techniques to their advantage. 

San Antonio Police released a warning about prospective thieves using power amplifiers to gain access to the signal within fobs and asking drivers to practice caution. 

The National Insurance Crime Bureau also conducted studies involving new technologies used to unlock, open, start and steal vehicles. The agency purchased a "relay attack" unit to attempt thieves' techniques on cars and trucks using keyless remotes and push-button ignitions, finding that a "mystery device" could open 19 of 35 vehicles.

At Cambridge Auto Shop, Terry Toller says he's seen drivers wrapping fobs in tin foil as a technique to prevent signal theft. Some experts say it can weaken the signal, preventing hackers from retrieving or amplifying the signal. 

But Toller also suggests continuing conventional techniques to prevent auto theft. 

"My theory is if they want to get into your car, they’re going to get into your car, regardless," Toller said. "That might make it a little cleaner or easier for them, but they’ll break your window if they see something they want. Park in well-lit areas, keep your car out of the dark sides of the parking lot or way in the back, (and) keep your belongings out of your car or put them in your trunk."

San Antonio Police could not confirm whether any cars have recently been stolen within city limits using this method, but the department says it is a concern and reminds people not to leave fobs in cars, even if it's a technological option.

The bottom line is that with a variety of devices, thieves are getting more creative—and drivers should use caution and common sense to prevent falling victim to more innovative schemes.