Wi-Fi can see through walls, researchers say

A Doppler-radar kind of system using Wi-Fi routers could strike a balance between society’s privacy needs and surveillance.

If you thought Wi-Fi was merely good for getting online, think again. Surveillance, military combat awareness and thwarting hostage-taking are three new uses for the technology.

Researchers say that they have figured out a way to use every-day home wireless Wi-Fi signals in a similar way to radar. They say they can see movement through walls with it.


“In a security situation, if somebody’s hiding in a room, as long as there’s wireless in there you might be able to detect them,” says Professor Karl Woodbridge, of University College London’s (UCL) Department of Electronic and Electrical Engineering, in a university-published document about the tech on the Internet.

Woodbridge is one of the developers of the idea. It’s just received an Engineering Impact Award at National Instrument’s NI Week 2015 meeting in Austin, Texas a few days ago.

Moving objects

The technology works by detecting the changing frequency of radio waves “reflected off a moving object,” UCL Business says in a 2012 article. UCL Business is one of the university’s technology transfer companies that supports and commercializes research and innovations coming out of UCL. It’s been promoting the tech, which the developers have been tweaking.

The radio receiver, then, included two antennas and a processing unit in a suitcase-sized kit, but more recent investments in software-defined equipment are allowing the scientists to make the receivers smaller.

Passive radiation

There have been similar Doppler radar-like detectors that have used “household communication bands, but these are active radars that transmit as well as receive,” according to IEEE Spectrum, who recently published an article about the technology.

The difference between those previous systems and the UCL one is that UCL’s technique uses only “passive radiation from Wi-Fi routers, using emissions in any of the IEEE 802.11 b, g, n, ac, ambient GSM and LTE mobile signals, and other sources,” IEEE’s Spectrum says.

“So there is nothing to betray the surveillance.” It’s not two-way.

And that’s a big deal, because it means the technology has possible uses in security. In fact, the U.K.’s Home Office (a kind of combination U.S. Department of Homeland Security and U.S. Department of Justice) is working with the team on future development, according to the website document.

Commercial uses

But it isn’t just quasi-military hostage releasing, or spying that the tech might be good for, though. Retail monitoring could detect where “people and crowds are moving about in stores, to inform the retail market about where people are moving and the products that attract them,” the document suggests.

Care monitoring is another possible use:

“The system can check that there’s movement around and flag up an alert if there’s been no motion in certain rooms for certain periods,” Woodbridge says.

Disasters are another scenario where the technology could be deployed—survivors’ chest movements caused by breathing under rubble could one day be detected.

Existing wireless infrastructure

But it’s the ubiquitous nature of Wi-Fi, along with other forms of wireless, that’s could be a major driver to the technology’s adoption.

Firstly the equipment is already deployed, and might ultimately be made to work with just a software update.

But also it’s using existing wireless infrastructure that’s not invasive, in other words it doesn’t use cameras and can’t identify actual people, so might check some boxes for privacy in our post-Snowden society.

Join the Network World communities on Facebook and LinkedIn to comment on topics that are top of mind.

Copyright © 2015 IDG Communications, Inc.