In what may be seen as a worrying development to those troubled by the growth of the surveillance state, researchers at the University of California, Santa Barbara have demonstrated that they can count people through walls using only Wi-Fi signals. Remarkably, the method doesn't require those being counted to carry wireless devices.
The method relies on RSSI, which stands for received signal strength indicator – a measure of the power of a radio signal. By using both a Wi-Fi emitter and receiver outside of the room of interest, the researchers say they can count up to 20 people in a room, even if they're milling around. The Wi-Fi equipment used is available off the shelf with minimal calibration needed ahead of use.
The presence and movement of people causes the RSSI to lower – drops that the researchers refer to as events. It's by analyzing the time between these events that the researches are able to count the people present. The method is accurate to within two people.
The researchers successfully tested the approach 44 times at three classrooms, a conference room and a hallway on the university campus. The tests involved counting people through wood, plaster and concrete walls.
Though surveillance is perhaps the first use that springs to mind, there are other compelling use cases for the technology. For example, it could help facilities teams to optimize the heating, cooling and lighting of a building, or events planners to monitor crowd safety in an events venue. And unlike some other methods, the approach can theoretically make use of equipment that is present already thanks to the ubiquity of Wi-Fi.
This latest development builds on the team's prior work in counting people with Wi-Fi and other radio signals, but only now are they able to do this through walls.
It's worth noting that the team is also researching imaging through walls using Wi-Fi-carrying drone aircraft, so surveillance is clearly an area of interest for them. We've asked how the team's research is funded and will update this article if we find out.
The team's researcher paper, Crowd Counting Through Walls Using WiFi, has been published by the IEEE and is available to read online (PDF link).
You can see a video on this research below.
Update September 27, 2018: UCSB professor Yasamin Mostofi has replied to let us know the research is funded by the US government's National Science Foundation.
Source: University of California, Santa Barbara