BRIGHT IDEA: Israelis ‘listen in’ on light bulbs, spy on conversations hundreds of feet away

New ‘lamphone’ technique lets you hear what’s going on hundreds of feet away by monitoring the vibrations of a light bulb in a room where people are talking.

By Paul Shindman, World Israel News

Researchers from two Israeli universities have figured out a new technique to eavesdrop on conversations by analyzing the vibrations of light bulbs, Wired magazine reported.

Teams from Ben-Gurion University of the Negev and the Weizmann Institute of Science in Rehovot recorded the tiny changes in light output from a light bulb due to vibrations caused by sound waves, then processed the data to reproduce the noise, including any conversations, that caused the light bulb to vibrate.

The new technique is dubbed “lamphone” (lamp and phone together) and uses a laptop, a small telescope and a $400 electro-optical sensor. The light vibrations are recorded, then processed in the computer, allowing one to listen to the words of a conversation or recognize what music is playing.

The new technique joins the list of ways to pick up information from a distance, especially conversations, like directional microphones, wiretaps, or putting your ear to a drinking glass you’re holding on to the wall of an adjoining room to pick up the vibrations. At the far end of the spy spectrum is a technique that bounces laser beams off of windows to pick up conversations inside a room.

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“Any sound in the room can be recovered from the room with no requirement to hack anything and no device in the room,” Ben-Gurion researcher Ben Nassi told Wired. “You just need line of sight to a hanging bulb, and this is it.”

The researchers used a series of telescopes equipped with an electro-optical sensor and aimed them at a light bulb in a room. The light signals were then converted into a digital format and processed on a laptop to recreate the noise that was picked up.

The super-sensitive gear picked up vibrations as small as a few hundred microns. Filtering out background noise enabled them to discern test sounds, which included parts of a Donald Trump speech and a recording of the Beatles’ “Let It Be.” The resulting voice of Trump was clear enough to be transcribed by Google’s speech-to-text software and the song’s lyrics were identified by the name-that-tune app Shazam, the report said.

Should you make sure you have heavy blackout curtains on all your windows? Not yet, because the technique was only tried on a single bare hanging light bulb and the equipment was rudimentary. High priced gear might improve the capabilities, but energy saving light bulbs may prove much more difficult to listen in on than an old-style incandescent bulb.

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Stanford computer scientist and cryptographer Dan Boneh told Wired that lamphone is still a significant and potentially practical new “side channel” attack technique that exploits unintended leakage of information to steal secrets.

“It’s a beautiful application of side channels,” Boneh said. “Even if this requires a hanging bulb and high decibels, it’s still super interesting. And it’s still just the first time this has been shown to be possible. Attacks only get better, and future research will only improve this over time.”

Lamphone is similar to what researchers call a “visual microphone” whereby a video recording of any object in a room that vibrates, even a bag of potato chips, can be reconstructed into speech or music.

Nassi pointed out that focusing on a light bulb enables real-time spying and lamphone could be more practical as a spy tool that other methods.

“When you actually use it in real time you can respond in real time rather than losing the opportunity,” Nassi said.

However, Nassi said the researcher’s goal wasn’t to give spy agencies more ways to listen in on us, but to let people know what technology is capable of.

“We want to raise the awareness of this kind of attack vector,” Nassi said. “We’re not in the game of providing tools.”