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Comment by sponaugle | Hacker News Reader

This is a VERY controlled environment - and they used 20 passes of each person walking with direct knowledge of each person to train for identity. They did no tests with multiple people walking at the same time, or with any other external moving distortion effects (doors opening, etc) . This is very far from actual 'identification' of people in real public settings - and no doubt the cell phone everyone is carrying with them offers many orders of magnitude better opportunity. In a real crowded environment this would be nearly worthless.

The devices that reported BFI information were also stationary, and there were no extra devices transmitting information that would be conflicting.

A single camera would be much more effective.

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Yes, but things could be refined. With more resources and research thrown at it, it could become more versatile, that's why the title of the post says "could". And chances are, there are private and government entities already doing this. Research like this has been coming out for at least a decade now.

Even Xfinity has motion detection in homes using this technique now:

https://www.xfinity.com/hub/smart-home/wifi-motion

Yeah, it can and will be refined, but the major limiting factor is resolution. Wi-Fi radio waves are just too big to get a very clear image.

for now ...

No this is fixed by physics. 5ghz waves are about 60mm wavelength.

Your resolution limit is about 30mm as a result.

There are techniques that can reduce that limit when you have multiple signals, though whether they can be combined with this technique isn’t clear.

Wifi 7 includes 6Ghz band but fair enough

Add a nice prior from a photograph, combine multiple measurements and presto you can pick out a person from a crowd with reasonable accuracy. No?

It applies to the sensor size as well. Such as you need a 3m sensor to get 100px per radian, under ideal circumstances, unless I'm mistaken. (I think I'm not)

like i mentioned in another comment, do you really need good resolution for gait analysis? You also have people carrying their phones inside the house all the time, so you know what bssid is associated with that coarse movement. and if you have access to their ap/router combo, you can tell what IP that device has and what domains it's been visiting.

Let's say you visit a friend in a different city, the same ISP controlling their router, can use your mac, but even if you turn off your wifi or leave your phone in your car, your volume profile and gait can betray you. how you sit, how you lean, how you turn. I'd wager, if 6-10 distinct "points" can be made out and associated with a person, that's all that's needed to uniquely identify that person after enough analysis of their motion, regardless of where they go in the world.

Imagine if they're not using one AP, but using your neighbors AP as well, two neighbor APs and your own can triangulate and refine much better.

6 cm is too big? It’s big enough to get an idea of people moving around. And what about the 5 cm wave of 6G Wi-Fi?

But then we can talk about all the millimeterwave signals that are bouncing around everywhere.

What about 5G cellular? It already supports millimeterwave bands!

Only if wifi is radically increased in frequency, power, directionality or antenna size. And i mean way beyond practicallity. It would be easier to identify people by the sounds of thier footsteps, something easily done through anything with a microphone. With three microphones, you can track that movement to the inch.

or if wifi from mobile devices, and your neighbor's APs and their wifi devices is collated to build a fine-enough picture of movements.

This has already been an area of research, both publicly, and most likely in private/government defense research. In a targeted situation, i.e. surveillance of a household of 6, this would work easily enough...but I doubt there is enough information to provide reliable (high AUC) tagging of ID in a public scenario oh hundreds to thousands of individuals.

if it's a public scenario, you don't need that, they're using wifi on people's persons to id them. The concern is more gait analysis, and by some accounts even lip reading is possible with mm-wave 5g.

https://www.theregister.com/2025/07/22/whofi_wifi_identifier...

> Researchers in Italy have developed a way to create a biometric identifier for people based on the way the human body interferes with Wi-Fi signal propagation.. can re-identify a person in other locations most of the time when a Wi-Fi signal can be measured. Observers could therefore track a person as they pass through signals sent by different Wi-Fi networks – even if they’re not carrying a phone.. their technique makes accurate matches on the public NTU-Fi dataset up to 95.5 percent.

That’s 95.5% accuracy with a 16 person dataset in a highly constrained environment.

Wi-Fi uses long wavelengths, you can cancel out the noise with one person but crowds are all distorting the same very weak signal here. 5Ghz = 6cm, visible light is 380 to about 750 nanometers.

I bet there is.

Off the top of my head, I bet body composition combined with gait analysis would be enough to uniquely identify an individual.

Xfinity's is sensitive enough to configure for animals or humans under 40-70lbs, I forget the exact number.

From my minimal research, it could be pushed a lot further.

What I'm particularly interested in is the edge case scenario of duplexes and apartments, where neighbors are unwittingly subjected to surveillance. There is little more to their routers than firmware to impart these capabilities. No reason to think it won't become common, and there are a handful of other companies basically offering just this as a service.

Strange times.

Edit: I should have mentioned the obvious, that pesky thing no one wants to address... When AI is added to this tech, it will get grotesque. Gait recognition, behavioral patterning, etc. Not something to sneeze at.

Possibly what was used to watch Maduro, along with synthetic aperture radar etc.

> Even Xfinity has motion detection in homes using this technique now

WiFi presence detection is a completely different problem. If the WiFi environment is changing past a threshold, return a boolean yes or no. It can't actually tell if someone is present or if the environment is just changing, such as a car driving close enough to reflect signals back in a certain way.

Doing mass surveillance where you detect individual people in a random home environment isn't the same thing at all. All of these "could" claims are trying to drawn connections between very different problems.

You'll have to explain that a bit more. Isn't the threshold detection analyzing radio signal data? For identifying people, you don't need to reconstruct their face or fingerpring using that data. you just need to fingerprint them.

With gait analysis for example, it's only looking at a handful of data points, the way we walk is very unique. lip-reading, i can see how that's a stretch, but out movement patterns and gait are disturbances in radio waves. If you're using just one person's wifi, that sounds difficult, but if you're collecting signal from multiple adjacent wifi access points, it's more realistic to build a very coarse motion representation, perhaps with a resolution no finer than 1 cubic ft, but even with more coarse representations, gait can be observed.

Even gait aside, the volume profile of a person and their location in the house alone are important data points, couple that with the unique wifi identifier or IP, you can make a really good guess at who the person is, and what room they're in.

Insufficient granularity of data

the article is off-base with wifi. the real story is in 6G cellular.

there is a working group at 3gpp, an EU-funded research group (6th sense, Open6GHub), universities (NCSU, Bristol), and many companies working very hard right now on proposals to include "integrated/joint sensing and communication" (ISAC/JCAS) in the 6G spec.

ISAC means adding mmWave to 6G (ostensibly for speed, but also) to build a high-fidelity 3d realtime "digital twin" of the real world that can see through walls, owned and operated by your telecom provider.

> A very exciting innovation that 6G will bring to the table would be its ability to sense the environment. The ubiquitous network becomes a source of situational awareness, collating signals that are bouncing off objects and determining type and shape, relative location, velocity and perhaps even material properties. With adequate 6G solutions for privacy and trust, such a mode of sensing can help create a “mirror” or digital twin of the physical world in combination with other sensing modalities.

https://www.nokia.com/about-us/newsroom/articles/nokias-visi... https://www.bell-labs.com/institute/blog/building-network-si...

there's been a testbed deployment in a German hospital for "non-invasive" monitoring of vitals; which sounds to me like it can literally see a heartbeat.

https://www.nokia.com/about-us/news/releases/2024/12/17/noki...

truth is, this is the nature of wireless radios. we can't keep improving bandwidth and latency without also turning the radio into a camera. i'm disturbed by the inevitability.

Bruce Wayne implemented this almost 2 decades ago in The Dark Knight. EU innovation moving at a snail's pace as usual /s

> ISAC means adding mmWave to 6G (ostensibly for speed, but also) to build a high-fidelity 3d realtime "digital twin" of the real world that can see through walls, owned and operated by your telecom provider.

"See through walls"

There used to be a great video on youtube of a very high power 60GHz signal being blocked by a door. Sad I can never find it. E Band isn't much better.

IIRC the 60GHz radio is being left out of a lot of 5G deployments because the slight benefits don't outweigh the cost.

This is a pretty common thing for mmWave (or near mmWave) to be deployed with massive fanfare and then be slowly phased out of existence. I am decidedly not writing this on a WiGig docking station.

I dont see telcos wanting to constantly broadcast extra mmWave for little to no added benefit, especially not in all directions. Likewise, regulators are going to choke on that. And the class/band license schemes would have to be updated, to remove interference from devices already using those bands as they are about to have a constant background level of interference. E-Band PTP users, of which there are many, wont give up their high capacity links to weird 6G omni broadcasts without a fight.

I tell you what however, having a button you can press that would map the environment for alignment sounds like a maybe use case here. Better than a camera for detecting new obstructions when links go down.

They might also add more bands to the whole automatic MIMO backhaul trick they have been pursuing.

yeah there's some truth here. from what i understand, the radios that give the best "imaging" are also the least resilient for data -- you need basically line-of-sight. and 5G did have some optional ULF "add-ons" that basically never got used because the tradeoffs for speed to signal integrity were poor.

it won't start as a mass deployment -- just focused on stadiums, airports, government buildings, etc.; maybe some authoritarian states will attempt mass deployments, but the cost will be an obstacle. also, my read is that western telcos aren't interested in owning a surveillance tool because they know their governments won't let them keep it.

hopefully 6G won't be the end of physical privacy. but it will prototype the end of physical privacy -- and i think it will end up being just a matter of time from that point on, unfortunately.

I just dont see the benefit, unless you are installing a 6G device in every room of your house.

Which is probably the target case here. 4G had light adoption by smaller telcos, 5G has some self installable repeaters, but most of the plans for 5G to spread to self installed / class license hardware were all vapourware. 6G might have some backing pushing them into trying to find more ways to sell 6G devices, and having put up a bunch of 6G certified (but class license only) devices in your home, it would be cool if you could see some biometrics, and hook the system into home automation for surveillance and determining whether the lights go on.

But without that in home capability, and massive spread of deployed devices I just dont see the surveillance utility. Especially if your town has lots of awnings and trees.

Great. Now you’re telling me the chicken wire embedded in my walls isn’t sufficient, and I’m going to have to go with grounded sheet metal?

underground bunker

Yes, you won't be able to do this on normal wifi traffic typically either, you need to send specific packets at a high enough rate (in between normal internet traffic) in order to sense with any accuracy, as I also remarked earlier: https://news.ycombinator.com/item?id=46976849

Yea, that makes sense as you would need quite a bit of information across a reasonable temporal range if the identifying qualities are movement related. Very interesting.

There'll be an update where a first responder can send a special packet to an SSID that will enable these high rate packets without needing to join the wifi. It'll be secure where only the good guys will know about it so that it won't be able to be used nefariously. /s

Yes but this is just the start and its already good enough for an ICE car to park outside your house and check if you're home and what room you're in.

They can do that by looking at the cars in my driveway/garage and or just watching the windows for any period of time. Plus my phone. If <insert 3 letter agency> agents are sitting outside of your house, they aren't going to drive away because you pull the plug on the router and suddenly deprive them of BFI packets.

Exactly. All of these stories using WiFi to detect things with high accuracy are just extreme machine learning demos.

Given a tightly controlled environment and enough training data, you can use a lot of things as sensors.

These techniques are not useful for general purpose sensing, though. The WiFi router in your home isn't useful for this.

WiFi AP's already do a lot of tracking and measurement just to improve signal fidelity and effective throughput. Why wouldn't those same techniques be useful for more general object tracking? Of course using a single AP to attempt to track movement in real-time is unlikely to have great results, but with several APs and enough compute triangulation should improve results.

> Why wouldn't those same techniques be useful for more general object tracking?

These demos use machine learning to train against a known environment.

Basically, pattern matching changes in the signals against a very controlled set of training data.

You can use WiFi signals to detect that something is changing in the environment, but without the machine learning with controlled input data you don't know what it actually means. This is how WiFi presence detection works, but it won't tell you if it's a person moving through the house or your cat walked in front of the router.

today's tech demos are tomorrow's everyday

Exactly. People are wrong to dismiss this as they're doing in this thread.

LLMs were useless back in 2021.

Unless they start storing data about your specific gait & posture, skull shape, limb dimensions and build up a "fingerprint" of your body.

You mean like those scanners at the airport?

Please submit full body 3D scan for verification, otherwise discord will lock you to the "kids only" section and mock you mercilessly.

You have nothing to hide unless you’re a pedophile plane bomber

Yes it's in a controlled environment not in a real world noisy environment. But this is more stealthy than a camera and could potentially work with non-line-of-sight or even through walls.

And based on that I could imagine with a combination of a camera and this method, you could train the model on data where both the camera and this method is seeing the individual and then continue to track them with the wifi sensing + the trained model even where the camera cannot see them anymore.

But yea real world is noisy, so it could be very challenging.

Yeah this is one of those "cool demo" research results that is completely impractical in the real world that is sold (probably by university PR departments) as an actual viable technique that might have real-world implications.

We've seen it before with things like taking photos around corners.

And no, it isn't like the Wright flyer and a bit crap now but in 40 years we have jet planes. This will never get significantly better.

Yeah I've seen this same type of study done over the years with the same dire warning. But like you pointed out it's just extremely labor intensive when it's simply easier to attack phones, security cameras or any other smart device that can be easily hacked. Or just install your own bugs.

Would not be surprised to see this get more traction right now due to the political climate.

If I was interested in mass surveillance I would combine the radio data (WLAN, BT, ...) with the camera feed. If you then see the same person with ML, you can correlate that with radio's. You can even do that with cell towers with anonymous SIM, especially if combined with public transport camera feed or ALPR/ANPR.

HEADLINE: Electromagnetic radiation can be used to see!!!!

Right, that's what your eyes do. Radio is much longer wavelength than visible light (~5-10cm). So at best it offers extremely crappy resolution unless - you're doing something clever with second order information.

Well nowadays you individually track by using mac addresses and other network information from the devices within range. Cisco has some creepy real time maps of your location with each person walking around and all their previous visits etc

Modern phones connect with a randomized MAC address. So yes, you can track a person around, but you will need another system (like the WiFi login page) to match MAC to identity.

Really? I thought it was only I phones that did that though?

windows 11 also has it.

Android has been doing this for a while, too

Saw a system like this at a Podunk, nowhere, USA police station over a decade ago. It had high fidelity maps of peoples comings and goings based on Bluetooth and WiFi MAC IIRC. And some kind of API backend to look up identity based on those identifiers, not sure to who.

You could for example flag a location (house) and get a list of all of the comings and goings over the last x months, then look them up by identity. You could also flag when an individual was in proximity to another, or when someone turned on, off or switched phones.

I’m sure it amounted to illegal surveillance and would be inadmissible if any of it was done without a warrant, but it would be beautiful for parallel construction. (How is that even constitutional???)

It apparently relied on some kind of infrastructure deployment that consisted of “traffic cameras” and “satellites” ( I’m certain not of the spacecraft type) that I assume were just small receivers mounted on street lights, since the streetlights were almost completely replaced at the same time as the cameras were put in, by the same out of state contractor.

I was there to change out a bad SSD and do a RAM upgrade on one of the servers. I don’t imagine the technology has become less invasive.

If you have a phone or carry active Bluetooth devices, assume you are 100 percent tracked 100 percent of the time.

If you want to not be tracked I wouldn't even trust airplane mode. With just a SIM pinging towers already a lot can be done. With airplane mode I'm just being paranoid but I never tested radio emissions myself with it disabled so I'd just leave my phone at home if I was really worried about it.

Turning your phone off (airplane mode or power down, which sign out of networks) or lighting up a new one in the same location as an old one was turned off are treated as significant events in these systems and can be configured as an automatic flag for investigation.

If you care, slip it into a faraday bag instead of turning it off or going into airplane mode and you won’t be flagged nearly as likely. People rarely use airplane mode or turn off their phones in situations where it doesn’t provide a useful clue about activity.

There is a huge overlap between surveillance platforms and behavior analysis / data brokers.

When it comes to capability, the phrase “it’s the worst it’s ever going to be” comes to mind.

This is going into the next Wifi standard specifically to get this data off of normal wifi traffic.

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