As Maggie Jauregui was getting ready for a date last November, she was simultaneously blow drying her hair and chatting with her boyfriend over a walkie talkie—the sort of electronic gadget that the hacker couple enjoy messing around with. Suddenly, the hair dryer’s plug began to violently vibrate against the wall socket, then spark and release a curl of black smoke. “My jaw just dropped,” Jauregui says. “I had no idea what had just happened.”

That fried plug, she soon figured out, was the result of radio waves the walkie talkie had transmitted at just the right frequency to create an overload of current in a coil of wire inside a component of the hair dryer called a ground fault circuit interrupter, or GFCI. And in the months that followed, Jauregui experimented with that hair dryer mishap until she honed it into a reliable attack: At the DefCon hacker conference in Las Vegas Saturday she plans to demonstrate on stage how a handheld directional radio antenna can be used to perform the same trick with the GFCIs integrated into household appliances like hair dryers and heaters or wall outlets, mischievously switching them off or making the plugs shake, spark and melt from as far as ten feet away. One of her tests is shown in the video below.

Jauregui’s trick isn’t exactly new: Electricians and ham radio enthusiasts have warned for years that some GFCIs are vulnerable to occasional radio wave interference. But she plans to demonstrate the trick in front of DefCon’s security-focused audience to show that it still works on many modern devices. She mostly sees the plug-frying attack as a hacker party trick—destroying the GFCI doesn’t even actually prevent the devices from working. But Jauregui argues it does demonstrate a real security problem, allowing anyone to remotely create a minor fire hazard or in some cases turn off power to sensitive equipment, even from the other side of a wall.

Jauregui's GFCI-frying radio antenna. Maggie Jauregui

“You just agitate these devices with radio waves for a short period of time and they overheat and blow up,” says Jauregui, who holds a day job as a software engineer for Intel but performed the radio research independently of the company. “That shouldn’t happen.”

GFCIs are designed, in fact, to serve as a safety measure. The modules work as circuit breakers, cutting the power to devices if they detect that a gadget's current is flowing through a foreign body like a person or pool of water; GFCIs prevent your hair dryer from electrocuting you if it falls into your bath, for instance. But many of the devices contain a transformer—–a ring of iron with electricity-conducting wire wound around it—–that Jauregui says can be induced by the right frequency of radio waves to carry a current. If that current is strong enough, a radio hacker can use it to trigger the device’s safety kill switch at will, as shown in a demonstration with a lamp in the video below. Or a different radio frequency can produce just enough current to make that internal switch vibrate without breaking the circuit and instead heat up until it short circuits and melts.

Newer designs of GFCIs are designed to be less susceptible to radio frequency. But Jauregui says she found 12 modern devices that still use older, vulnerable patents. In her testing, she says she once accidentally fried the GFCI in her next-door neighbor’s hair dryer, through her townhouse’s wall. And she even successfully tested her attack against the hair dryer in her room at the Rio hotel in Las Vegas, where the DefCon conference takes place.

In her talk, Jauregui says she won’t reveal the type of radio antenna or frequencies her hack uses, or even the brands of devices that were susceptible. In many cases, she admits, the hack is mostly harmless—–gadgets with their GFCIs burned out continue to work, albeit without the safeguard against electrocution the component is designed to create. But in some cases she points out that medical devices or other critical equipment might be plugged into GFCI-connected wall sockets, with more serious consequences. “What if it’s an old lady who lives alone and depends on her respirator?” Jauregui asks.

With a bigger power source and an amplifier, Jauregui says the attack could even be extended well beyond her antenna’s ten-foot range. If nothing else, the trick has enormous potential for creating mass confusion among unsuspecting hair dryer owners, which Jauregui says she’d like to avoid enabling. She says she’s still working to distinguish exactly which devices have the older form of GFCI, but plans to alert the companies that sell devices with the vulnerable component.

“This is definitely not a talk on ‘how to annoy your neighbors.’” Jauregui says. “It’s a warning to watch out and to try to be safe with these devices.”