back to article Put your tin-foil hats on! Wi-Fi can be used to guesstimate number of people hidden in a room

Wireless network gear can be used to estimate the number of people hidden behind walls, according to fresh research out of America. Saandeep Depatla, a PhD student, and Yasamin Mostofi, a professor of electrical and computer engineering, both at the University of California, Santa Barbara, were able to figure out more or less …

  1. Zola

    Good grief that voice...

    Had to mute the video.

  2. Anonymous Coward
    Anonymous Coward

    Who needs a tin foil hat? I'm just going to up my water consumption as WiFi struggles to go through water.

    1. Fred Flintstone Gold badge

      I'm just going to up my water consumption as WiFi struggles to go through water.

      Most sysadmins are waaaay ahead of you. Guess what contains a lot of water?


      1. Anonymous Coward
        Anonymous Coward

        I dunno... a bucket of piss?

    2. LewisRage

      ...WiFi struggles to go through water

      Which will make you more noticeable in this test.

      The trick seems to be to dehydrate so wifi passes more easily and you become invisible.

  3. Wolfclaw

    WIFI security system anybody ?

  4. Charlie Clark Silver badge

    It’ll be a while before something like this is practical, but there are obvious areas where it would be useful.

    I can't think of any areas where this would be more useful than other existing approaches. In particular, the example of bodies in a building shows a lack of understanding of how the technique works: you can't just point a wifi beam at something, you need a baseline.

  5. Pete 2


    > The system [paper PDF] then computed the slight changes in the Wi-Fi network strength over time into a guesstimate of the number of people in the room

    It is a fairly gross assumption that the only "bodies" in a room are human.

    1. Teiwaz Silver badge

      Re: Woof!


      Count the number grazing cattle staring into the social network abyss, chewing the cud of mindless drivel.

      1. Anonymous Coward
        Anonymous Coward

        Re: Woof!

        Herd mentality?

        1. Teiwaz Silver badge

          Re: Woof!

          Herd mentality?


          I'm sorry, I was busy tweeting.....and two slices of toast for breakfast....

    2. LDS Silver badge

      "only "bodies" in a room are human."

      Looking at some of my colleagues you may be right. But I'm also sure not many have big animals in a room, albeit it's true some dogs are big enough - yet being biped or quadruped may change how the beam is intercepted.

      Cats. on the other hand, I'm sure are small enough to merge with the noise especially when they sleep, and anyway their whiskers would warn them.

    3. Cuddles Silver badge

      Re: Woof!

      "It is a fairly gross assumption that the only "bodies" in a room are human."

      What else would they be? If this is being touted as a way to count how many customers are in places like shops and cafes, there are unlikely to be any other large animals moving around inside. The number of guide dogs will be well within the normal margin of error, and outside some kind of Jumanji situation what other possibilities are there?

      1. I ain't Spartacus Gold badge

        Re: Woof!

        Well I often walk Spot, my pet elephant, to the shops.

        You'd think he'd worry passers by. But they take much less notice of him than my pet lion.

    4. unbearable

      Re: the only "bodies" in a room are human.

      Generation 8, coming real soon in 2035, of the technology will have the ability to distinguish pets from humans (including human pets) using a chip in the collar.

      1. Joe W Silver badge

        Re: the only "bodies" in a room are human.

        Whose collar?

    5. OssianScotland Silver badge

      Re: Woof!

      My collies would like to upvote you too

  6. WibbleMe

    Wast there something like that in "Batman Begins"?

  7. Rich 11 Silver badge

    how many enemies or civilians

    Shouldn't that be 'how many enemies and civilians'? All you're getting is a total, to help you decide if your surgical strike is worth the cost of a smart missile. The decisions on whether killing all the civilians just to kill your enemies is either moral or will be worth the negative publicity are entirely separate.

    1. David Shaw

      Re: how many enemies or civilians

      I might have built a synthetic aperture radar based on WiFi, for detecting "moose/elk" passing across the forested european border to a very large autocratic regime, or vice-versa

      Now I've recently seen similar devices along some of the wilder roads in the Alps, checking for deer & wild-boar and flashing signs at cars and beaming awful noises at the wildlife. Only seen one 'tripped' but there were no heffalumps in sight.

  8. Anonymous Coward
    Anonymous Coward

    "Using drones could open the technology to military applications"


    Thought free writing, it's the new black.........

  9. ivan5

    It says this is used from outside the room. How well does it work when the walls are 1 metre thick solid stone? Or is this something that only works in the US timber frame with plasterboard covered walls?

    1. Anonymous Coward
      Anonymous Coward

      Even houses with meter thick stone walls typically don't have meter thick stone interior walls. They were testing from an adjoining room, not outside the structure - and they were doing it through not just wood but also plaster and concrete walls. I'm sure their concrete walls weren't a meter thick, but still.

    2. Pookietoo


      It had better not be foil-backed plasterboard.

  10. WibbleMe

    You have to remember that mobile phone masts also double as a mini radar station, that techs already out there.

    1. phuzz Silver badge

      Given the wavelengths that mobile phones use, it's not that much use as radar, except at short distances like this study. Not to mention that mobile masts are usually omnidirectional, making them more useless as a radar.

      1. Charlie Clark Silver badge

        more useless as a radar.

        Except for rain. I thought there was research being done using base stations to get very granular data on humidity?

      2. Joe W Silver badge

        Re: omni directional

        You mean like a simple synthetic aperture radar?

    2. David Shaw

      You have to remember that mobile phone masts also double as a mini radar station

      the analysis of GSM disturbances allegedly detected stealth aircraft, pre Bosnia

      some search terms "GSM opportunistic emitter bistatic multistatic radar" . quite a bit of (simple) MATLAB signal processing can extract a lot of info from any available transmitter, parasitically

      I've no real idea what the military call them, from the 'humanitarian' radar side we also used them for avalanche/mudslide and volcanic eruption prediction. Hopefully the new UK Space Radar sat can also do some of that

  11. Destroy All Monsters Silver badge

    Yeah, about that.

    Using drones could open the technology to military applications. Such a system could help armies scout out how many enemies or civilians were in a particular building before ordering drone strikes.

    You mean AFTER ordering a drone strike?

  12. Jamie Jones Silver badge


    Now I don't just have to worry about hackers, I have to worry people finding out I have no friends.

    1. I ain't Spartacus Gold badge

      Re: Great....

      There's nothing stopping you having a few store dummies or inflatable people about the place as decoys...

      1. DropBear

        Re: Great....

        I seriously doubt inflatable people would interfere much with the signal - unless you inflate them with some kind of liquid instead of a gas, at which point this becomes too kinky even for me, and that's without going into structural issues with an object that was not meant to support the weight of a liquid inside itself...

  13. Anonymous Coward
    Anonymous Coward

    OH NO!!

    They have just RUINED hide and seek!!

  14. Natalie Gritpants Jr

    "the team could detect up to 20 people walking casually in a room"

    I'm OK then, I march everywhere.

    1. DropBear

      Re: "the team could detect up to 20 people walking casually in a room"

      Huh... the ministry of funny walks may just have a justifiable future after all...!

    2. Flakk

      Re: "the team could detect up to 20 people walking casually in a room"

      Yes, but how does their equipment compare to that of the Ministry of Housinge's Cat Detector Van?

  15. Anonymous Coward
    Anonymous Coward

    When someone stepped directly between

    did the research test a scenario with a bloke plus a duo of sex dolls strapped to himself, to confuse snoopers, of course? Inquisitive tinfoil hat wants to know!

  16. maffski

    ... walking casually in a room...

    I don't know about you, but I don't actually spend a whole lot of time walking casually in a room. And this doesn't work at all if your sat down.

    I hope this paper wasn't responsible for his PhD. It doesn't exactly move the state of the art forward does it? It's exactly the same transit method as people have been using to detect exo planets for two decades. In fact you can do it without wifi anyway - look at a window and people passing will reduce the transmission from the ceiling lights.

    The only time I can think where this might work accurately is during a particularly vigorous earthquake.

  17. Tom Wood


    "Wi-Fi base stations could be used in shops, offices, hotels, cafes, and so on, to work out how many people are present at a given moment of the day"

    Don't most of those places already have CCTV which could be used for such purposes... Probably more reliably?

    1. Charlie Clark Silver badge

      Re: CCTV

      CCTV isn't used for footfall, you can just use motion detectors for that and you can passively detect mobile phones fairly easily.

      However, there are apparently tests using cameras to read behaviour and interests…

  18. StuntMisanthrope

    Ground Floor Wine Cellar - Navajho 1868

    System Access Management, per device on location by time. It's all acronym soup to me. #whatsyournameagain

  19. ravenviz

    "enemies or civilians"

    Note 'or' not 'and'.

  20. spold Silver badge

    Water - Obfuscation

    Mitigation by obfuscation. Place large bags of water around the office and a paddling pool in the meeting rooms (bring your own rubber duck).

    Put one in your own office/cube and no-one will notice you buggered off down the pub. Just put a smiley face on it.

  21. unbearable

    Holy life form sensors

    Star Trek, you've done it again.

    1. DropBear

      Re: Holy life form sensors

      Not "life". Just motion...

  22. Kay Burley ate my hamster

    You can get detail too...

  23. The Monitoring Guy


    This is years old. :/

  24. ukgnome

    Judging by the awesome performance of the WiFi at work I reckon the office has nearly 1 billion people in it.

    1. Joe W Silver badge

      ...or you are "heavy bags of water" - Pitr (userfriendly) did some experiment along these lines.

  25. Florida1920
    Big Brother

    Conductive paint

    I predict an increase in sales of the stuff in certain quarters.

    1. Anonymous Coward
      Anonymous Coward

      Re: Conductive paint

      Anywhere that will care about this particular attack will have already cared about general signal leakage and already RF sealed any important rooms/buildings.

  26. mrobaer

    3 years ago...

    Isn't this just about the same thing MIT did waaaaaaaaaay back in 2013?

    And then improved on the concept a bit in 2015?

  27. Tomato Krill

    Is this not basically a long winded way of using heat sensitive photography - or looking through the windows fornt that matter?

  28. Jason Bloomberg Silver badge

    "It's giving us cancer!!!"

    There you go; that will kill the idea stone dead.

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