![]() "It’s like we invented the shotgun, and this work is like, ‘We improve on the shotgun, we give you a rifle,'" Davis says. He says he has always suspected that using a different sort of camera, purpose-built for this sort of optical eavesdropping, would advance the technique. "This definitely takes a step toward something that’s more useful for espionage," says Abe Davis, one of the former MIT researchers who worked on the Visual Microphone and is now at Cornell. Aside from the Rubik’s cube, they tested the trick with half a dozen objects: a silvery bird figurine, a small polished metal trash can, a less-shiny aluminum ice-coffee can, an aluminum smartphone standard, and even thin metal venetian blinds. With a powerful enough telescope, their method worked from a range of as much as 115 feet. The researchers showed that in some cases, using a high-end analog-to-digital converter, they could recover audible speech with their technique when a speaker is about 10 inches from a shiny metallic Rubik’s cube and speaking at 75 decibels, the volume of a loud conversation. The researchers could then correlate those tiny light changes to the object's vibration in a room where someone is speaking, allowing them to reconstruct the nearby person's speech. That photodiode was then connected to an analog-to-digital converter and a standard PC, which translated the sensor’s voltage output to data that represents the real-time fluctuations of the light reflecting from whatever object the telescope points at. In their experimental setup, they attached a photodiode, a sensor that converts light into voltage, to a telescope the longer-range its lenses and the more light they allow to hit the sensor, the better. ![]() The researchers' trick takes advantage of the fact that sound waves from speech create changes in air pressure that can imperceptibly vibrate objects in a room. "And the beauty of it is that we can do it in real time, which for espionage allows you to act on the information revealed in the content of the conversation." "We can recover speech from lightweight, shiny objects placed in proximity to an individual who is speaking by analyzing the light reflected from them," says Ben Nassi, the Ben Gurion professor who carried out the research along with Ras Swissa, Boris Zadov, and Yuval Elovici. ![]() ![]() Unlike older experiments that similarly watched for minute vibrations to remotely listen in on a target, this new technique let researchers pick up lower-volume conversations, works with a far greater range of objects, and enables real-time snooping rather than after-the-fact reconstruction of a room's audio. By pointing an optical sensor attached to a telescope at one of those shiny objects-the researchers tested their technique with everything from an aluminum trash can to a metallic Rubik's cube-they could detect visible vibrations on an object's surface that allowed them to derive sounds and thus listen to speech inside the room. Now one group of researchers offers a surprising addition to that list: Remove every lightweight, metallic object from the room that's visible from a window.Īt the Black Hat Asia hacker conference in Singapore this May, researchers from Israel's Ben Gurion University of the Negev plan to present a new surveillance technique designed to allow anyone with off-the-shelf equipment to eavesdrop on conversations if they can merely find a line of sight through a window to any of a wide variety of reflective objects in a given room. Consider even stripping internal microphones from your devices. Put your phone in a Faraday bag-or a fridge. The most paranoid among us already know the checklist to avoid modern audio eavesdropping: Sweep your home or office for bugs.
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