I have a room (a waiting room) about 10x10 meters and I would like to locate people in there. The ceiling in the room is really high, so I can place a radar above in any height I want. My questions:

  1. Is it possible to use some ready/made radar/lidar solution to detect what seats in the room are currently used by people?

  2. Is it possible to detect people moving in the room on the fly (~30fps)?

  3. Is it safe to use radar on humans?

I know there are papers on this topic. However, I am not sure if there is any reasonable inexpensive solution for ordinary people. Something I can plug in PC and read raw data to process in any software I develop.

Further info:

There will be cameras. This measurement should be a complement to the camera machine vision to make it more reliable. I have experience with development of machine vision systems in difficult environments (mainly industry environment) and they have never worked as intended.

I also thought about tensometers, accelerometers, or microphones in the chairs to just locate sitting persons, but I would like to avoid collecting 20-60 channels.

  • $\begingroup$ As detail changes in the camera view the image size changes... we used that once. But are you allowed to irradiate subjects? $\endgroup$
    – Solar Mike
    Jun 18, 2020 at 6:23
  • $\begingroup$ @SolarMike I edit my question. $\endgroup$
    – matousc
    Jun 18, 2020 at 11:32
  • 1
    $\begingroup$ Honestly I do not deem irradiating people a good idea, especially if it's a kind of waiting room where long stay would be normal. Not to mention legal aspects, even if radiated power could be very low you should probably undergo long NHCS verifications. IMHO a second, or even more, indipendent vision system, different cameras, different view angle, different processor could be used merging and cross analysing datas $\endgroup$
    – carloc
    Jun 22, 2020 at 5:09
  • $\begingroup$ Indoor motion detectors have been used for security & other reasons in offices & homes for decades. It might be possible to adapt this technology for your requirements. $\endgroup$
    – Fred
    Mar 19, 2023 at 1:38

3 Answers 3


Any reason why you want to use radar? Why not use image processing from a visible-light camera, or even an IR camera?

Edit in response to the additional details you provided: I have done some work on image comparison for intruder detection systems and is hard to get it working as intended too. Because I am running my machine vision system on platforms with low computational power, in the end I have to use very simple rule-based algorithms which often give false positives. But I need the resolution visible-light cameras give so I have to stick with them.

If you just want to locate people in the room, my suggestion would be to use IR cameras. They are not as niche as they sound - it is possible to modify commercially available cameras to infrared ones (Google it). Then you may assume that any hot spot on a seat is (probably) a person.

  • $\begingroup$ I edit my question. $\endgroup$
    – matousc
    Jun 18, 2020 at 11:32

Technically, there are multiple options for detecting people in rooms such as LIDAR, RADAR or Ultrasound sensors (at head level). However, it is important to also consider the ethical and professional implications of using these sensors.

It is important to recognize that any device emitting power should only be used when absolutely necessary. This means that before deciding to use any of these sensors, it is necessary to evaluate whether their use is justified and whether there are other alternative options available that could be used instead.

Additionally, it is important to ensure that any data collected through these sensors is being used in a way that is respectful of individuals' privacy and autonomy. This means that appropriate safeguards must be put in place to protect the confidentiality of the data, and that individuals must be informed about the purpose of the sensors and their data collection.

A passive and somewhat privacy-protecting option can be "thermal/infrared" sensors. They lack the resolution to identify people, but they work perfect for detecting people.

There are also articles about passive Radio signal receivers (e.g. WIFI) for detecting people. Though, they are not as straightforward as a Thermal imaging solution.


I am wondering why not just use 2 light beams at the entrances and exits to count beam interruptions. It's a simple system but effective. With 2 beams broken in sequence you can tell which direction people are moving and drowns on which beam is interrupted first whether addition or subtraction occurs in the logic counter.

The distance between the pair should not exceed a human head distance from nose to nape.

  • $\begingroup$ This too can have errors. Children being carried by parents, someone in the shadow of another, people too close, etc. $\endgroup$ Jul 1, 2020 at 6:58
  • $\begingroup$ Agreed. No system is perfect. But it is preferable to high tech expensive equipment. If the beams are angled to create a crossing point in the vertical axis they may remove many errors such as your possible ones. A child in arms is difficult to detect $\endgroup$
    – Rhodie
    Jul 1, 2020 at 15:14
  • $\begingroup$ Unless the camera system is very sophisticated a child in arms will be difficult to detect by vision and probably impossible with radar/lidar. $\endgroup$
    – Transistor
    Jul 26, 2021 at 3:32
  • $\begingroup$ Nice idea, however it yields no information about where is the person in the room. $\endgroup$
    – matousc
    Mar 22, 2023 at 10:04

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