Cars with keyless entry systems are capable of searching for a wireless key fob that is within a couple feet of the vehicle, but car thieves can use a $17 "power amplifier" to boost the key searching capabilities, sometimes up to around 100 meters, and pull off a high-tech car break-in.

After almost becoming a victim of a high-tech car heist again, Nick Bilton over at The New York Times said he is now keeping the keys to his 2013 Prius in the freezer. There had been a rash of mysterious car break-ins near his Los Angeles address, including three break-ins to his own car; all cars involved had remote keyless systems that come with a wireless key fob which is used to unlock the doors and start the engine instead of using a physical key.

Recently, he was looking out his window and saw a girl hop off her bike and pull out "a small black device from her backpack. She then reached down, opened the door and climbed into my car." He ran outside and the girl split, but he was curious about the black device she used to open his Prius.

He called Toyota but got no useful info; the LAPD blew it off and told him that he must have forgotten to lock his car. However, he scored when he found a Toronto Canada Police public safety alert warning about "a spike in theft of Toyota and Lexus SUVs" that left no signs of physical damage at any of the crime scenes.

The Toronto Police alert said, "Investigators believe that the suspect(s) may have access to electronic devices which can compromise an SUV's security system." It urged "the public to be vigilant when securing their SUVs, even in their driveways. Using a locked garage is recommended and any spare keys for SUVs should be secured in a safe location."

Bilton contacted a security researcher at the Institute of Electrical and Electronics Engineers Public Visibility Committee, who said "some sophisticated thieves have laptops equipped with a radio transmitter" and use brute force attacks to find the correct and unique code of a car's key fob.

He found articles from 2012 about how car thieves took only three minutes to steal keyless BMWs by exploiting "features," before discovering an article about thieves using a "mystery device to unlock vehicles."

Finally, he got answers from Boris Danev, the founder of Switzerland-based 3DB Technologies. The girl most likely used an inexpensive "power amplifier" to break into Bilton's Prius.

Mr. Danev said that when the teenage girl turned on her device, it amplified the distance that the car can search, which then allowed my car to talk to my key, which happened to be sitting about 50 feet away, on the kitchen counter. And just like that, open sesame. "It's a bit like a loudspeaker, so when you say hello over it, people who are 100 meters away can hear the word, ‘hello,' " Mr. Danev said. "You can buy these devices anywhere for under $100." He said some of the lower-range devices cost as little as $17 and can be bought online on sites like eBay, Amazon and Craigslist.

What's the best way to protect your vehicle if it has a keyless entry system? The best way, Danev told Bilton, is to "put your keys in the freezer, which acts as a Faraday Cage, and won't allow a signal to get in or out."