Yasamin Mostofi asks us to imagine this scenario: police have video footage of a robbery. They suspect that one of the robbers is hiding in a house nearby.
Can a pair of off-the-shelf Wi-Fi transceivers, located outside the house, look through the walls to see who’s inside?
That’s easy to answer, since we’ve seen it done before.
In 2015, MIT researchers created a device that can discern where you are and who you are, detecting gestures and body movements as subtle as the rise and fall of a person’s chest, from the other side of a house, through a wall, even though subjects were invisible to the naked eye, by using the human body’s reflections of wireless transmissions.
Then, 11 months ago, a team of researchers at University of California Santa Barbara demonstrated using a streamlined set of technologies – just a smartphone and some clever computation – how to see through walls and successfully track people in 11 real-world locations, with high accuracy.
But here’s a new question: Can Wi-Fi signals be used to identify the person in the house? Can off-the-shelf hardware determine if whoever’s in the house is one of the people in the video surveillance footage police are scrutinizing?
Yes. UC Santa Barbara researchers are back again to show that they’ve built on their previous work: It can be done by analyzing people’s walking gaits and comparing them to the gait of whoever’s in the CCTV footage.
Mostofi, a professor of electrical and computer engineering at UC Santa Barbara, is the research lead behind XModal-ID: a proposed approach to using Wi-Fi signals to identify people from their walking gait.
The methodology and experimental results from Mostofi’s team, which will be presented at the 25th International Conference on Mobile Computing and Networking (MobiCom) on 22 October, show that Wi-Fi signals can be used to detect the gait of people through walls and to then match it to previously captured video footage in order to identify individuals.
As she describes in a YouTube video, XModal-ID uses only the power of a pair of Wi-Fi transceivers located outside a building.
It needs neither prior Wi-Fi or video training data of the person under surveillance, nor any knowledge of the area in which it’s going to be set up.
How it works
To identify individuals’ unique gaits, the researchers had to translate video into the wireless domain. To do so, they used what’s called human 3D mesh extraction. That’s an algorithm that extracts a 3D mesh that describes the outer surface of the human body as a function of time. Then, they added electromagnetic wave approximation to simulate the RF signal that would have been generated if the person was walking in a Wi-Fi area.
Next, they used a time-frequency processing pipeline to extract key gait features from both the “real” WiFi signal – i.e., the one that was measured behind the wall – and the video-based one. They compared the two spectrograms, which carry the person’s gait information, extracting a set of 12 key features from both spectrograms, and calculated the distance between the corresponding feature to determine if they matched.
In experiments conducted on campus in three different areas, they hit accuracy rates of between 82% and 89%.
For more details, check out the team’s project summary page, or you can read their paper.
Applications: surveillance, security and smart homes
The team suggests that there are several potential applications for XModal-ID:
- Security and Surveillance. The technology could be used by police who are searching for a suspect captured in video footage of a crime scene. They’ll need to position a pair of Wi-Fi transceivers outside a suspected hide-out building and then use XModal-ID to determine if they’re observing an individual who matches the one from the crime video. They can also use the existing Wi-Fi infrastructure of public places to detect the presence of the suspect, the researchers said… all of which would raise questions about warrantless search, I imagine…?
- Personalized Services. The researchers suggest that XModal-ID could also come in handy in a smart home, where the home Wi-Fi network could use XModal-ID and one-time video samples of each resident to identify who just walked into a room. Presto, switch on that person’s preferred music, adjust the temperature to suit, and set the lighting to his or her preferences.
Thomas
Creepy! If I ever rob a bank, my getaway vehicle will be a skateboard! Or I’ll practice walking like Kevin Spacey at the end of Usual Suspects.
Michael
And now we know how to identify you…
Polyhymnia
Quite literally what I was thinking, Kevin Spacey from Usual Suspects.
Great, so I’ll walk funny or with a limp if I ever plan on committing a major crime.
Bryan
The setup video depicted two perpetrators, carrying bags and firearms, effectively extending “arm’s length.”
Analysis is based on the singular metric of received power, so will it still be conclusive when multiple objects are in range? Also, anyone’s gait is rather altered by carrying a heavy bag, particularly on only one side. Those bags aren’t heavy.
Mahhn
So basically they are using Wi-Fi like a fish finder, but for hunting people.
The only dumb part is the example they offer. As if a hiding criminal is going to be walking back and forth waiting for detectives to figure out their normal walk, then setting up extra equipment, then processing the results of scanning all the buildings in the area from outside, then comparing the walk of everyone they scanned. Not even in a sci-fi movie would this happen, said the meat popsicle.
Jay
Sounds like a violation of a person’s illegal search and seizure
Phil Schaad
It appears that this technology can be applied to improve survalance and alarm systems by virtue of its ability to discretely identify regular occupants and authorized visitors to a monitored space by comparing real time data to a file of previously recorded data profiles representing people who are authorized to occupy the space at a given time. It should be possible to apply this technology to animals as well, therefore pets would not trigger false alarms. The appropriate hardware could be installed out of sight within the structure or in the immediate vicinity of the building spaces to be monitored.
This technology could potentially be used outdoors as well.
saxonrau
Personalised services sounds like hell – who wants the TV and music to switch whenever someone walks in?
ralphbragg
Definitely creepy but also kinda cool. Tech and convince always comes with some unforeseen trade offs usually at the cost of privacy, power and the environment. It’s the Tech Karma, Rule of 3’s -RAB
Steve
There is an apparent assumption that there will only be one person in the space, or at least some decent separation between people. And, of course, that the individual is walking around!
Still, that is a pretty decent accuracy rate. Has this been submitted to the Ministry of Silly Walks for proper testing?
Andrew
Wall hack for real life. The military applications of this for military operations in urban terrain are endless.
Watcher
The military has for over 15 years been able to see though shipping containers buildings ect. A friend of mine worked on the systems 10 years ago, it was in a car. He described it like what they see at airport luggage scanners. I expect it used some dangerous radiation since it wasn’t a public item. (maybe is public today?)