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Using Wi-Fi To Count People Through Walls (techcrunch.com)

Posted by msmash on from the how-about-that dept.

An anonymous reader shares a report: Whether you're trying to figure out how many students are attending your lectures or how many evil aliens have taken your Space Force brethren hostage, Wi-Fi can now be used to count them all. The system, created by researchers at UC Santa Barbara, uses a single Wi-Fi router outside of the room to measure attenuation and signal drops. From the release: "The transmitter sends a wireless signal whose received signal strength (RSSI) is measured by the receiver. Using only such received signal power measurements, the receiver estimates how many people are inside the room -- an estimate that closely matches the actual number. It is noteworthy that the researchers do not do any prior measurements or calibration in the area of interest; their approach has only a very short calibration phase that need not be done in the same area." This means that you could simply walk up to a wall and press a button to count, with a high degree of accuracy, how many people are walking around. The system can measure up to 20 people in its current form.

3 of 26 comments (clear)

  1. Ethical Implications by Aighearach · · Score: 3, Insightful

    If I use this to spy on my neighbors and find out they're being periodically abducted by the Asgard, should I tell them?

    Joking aside, the accuracy is around 2 people, and it can't tell you anything about distribution. So on average, you have no idea if there are people or not. But you can tell a crowded room from an empty room, at least in rooms that if empty would have a normal attenuation pattern.

    Pretty weak sauce. Old-school DIY radar on the same frequency is generally more accurate than this.

  2. Clickbait by Obfuscant · · Score: 2
    Clickbait for sucking eyeballs to advertising.

    It doesn't matter how much power you transmit outside a room, the received signal AT THE TRANSMITTER is not going to be attenuated by the people in the room. In fact, the received signal will depend ONLY upon the transmitted signal level -- the receiver and the transmitter are connected to the same antennas.

    This is patent nonsense.

    1. Re:Clickbait by Obfuscant · · Score: 2
      From an anonymous coward:

      The receiver and transmitter are not using the same antenna. They are on opposite sides of the room.

      From TFS:

      This means that you could simply walk up to a wall and press a button to count, with a high degree of accuracy, how many people are walking around.

      From TFA:

      The system, created by researchers at UC Santa Barbara, uses a single Wi-Fi router outside of the room to measure attenuation and signal drops.

      A single Wi-Fi router outside of the room cannot be on opposite sides of the room. A single Wi-Fi router outside the room likely has a pair of antennas, but they are separated by at most one foot. A receiving antenna one foot from a transmitting antenna is going to see predominately the transmitted signal direct from the transmitter antenna. The people INSIDE the room will have no effect on the signal.

      But a single WiFi router does not use one antenna for transmit and one for receive at the same time. That would be a stupid waste, since the receiver is only going to receive what the transmitter is sending. Why bother with that? No, the second antenna is for dual diversity -- the receiver can pick the best signal FOR RECEPTION by picking one of the two antennas.

      That means that the TRANSMITTER is not TRANSMITTING while the receiver is receiving. You CANNOT measure your own signal strength because you aren't receiving when you are transmitting.

      How would you even get a WiFi signal strength with just one antenna?

      By measuring the signal strength at that one antenna. You can't measure your own signal strength with one, two or a hundred antennas, because you aren't receiving your own signal, but you can measure another APs signal. That requires a SECOND WiFi router. This system unambiguously says "uses a single WiFi router". Is this a trick question or what?

      Now, if you aren't just using WiFi, you can do all sorts of amazing stuff with just one antenna doing both transmit and receive. We call that RADAR.

      And a standard Wi-Fi router has absolutely ZERO capability of doing RADAR. That's the point. You cannot have a single WiFi router that measures its own signal strength.