How your packet of crisps can spy on you

Aug 7, 2014

New video technology can listen in on conversations through soundproof glass


Everyday objects such as crisp packets and pot plants could soon be used for spying purposes, thanks to a new technology that monitors microscopic movements in the world around us.

A team at the Massachusetts Institute of Technology (MIT) has found a way to recover audio by scrutinising video of the tiny movements made by (almost) inanimate objects such as crisp packets when they are hit by sound waves.

The team found that, when analysed, the movements could be filtered to retrieve sound, opening up new ways of surreptitiously recording conversations or the possibility of retrieving audio from silent CCTV footage.

"When sound hits an object, it causes the object to vibrate," explained Abe Davis, the lead author of the study. "The motion of this vibration creates a very subtle visual signal that's usually invisible to the naked eye. People didn't realise that this information was there.

"Using only a video of the object and suitable processing algorithm we can extract these minute vibrations and partially recover the sounds that produced them letting us turn everyday objects into visual microphones."

Intelligence agencies can already monitor subtle vibrations in glass to listen in on conversations through windows, the Daily Telegraph says, but the technique doesn't work with soundproof glass. "This is the first time that anyone has been able to monitor vibrations using visual data and turn it back into the original sound," the Telegraph says.

The team demonstrated its findings by videoing the leaves of a pot plant while playing a recording of the children's nursery rhyme Mary Had a Little Lamb. Researchers were subsequently able to extract the audio by reading the small fluctuations in the movements of the plant's leaves.

The team was also able to "overhear" human speech by training a camera on a crisp packet from the other side of a soundproof glass door.

"This is new and refreshing. It's the kind of stuff that no other group would do right now," Alexei Efros, an associate professor at the University of California at Berkeley told the Telegraph.

"We're scientists, and sometimes we watch these movies, like James Bond, and we think, 'This is Hollywood theatrics. It's not possible to do that. This is ridiculous.' And suddenly, there you have it. This is totally out of some Hollywood thriller. You know that the killer has admitted his guilt because there's surveillance footage of his potato chip bag vibrating".

Sign up for our daily newsletter

Read more: