Washington: A Wi-Fi signal can be used to count the number of people in a given space, leading to diverse applications such as energy efficiency to search-and-rescue operations.

Researchers from University of California-Santa Barbara have shown that wireless signals can do more than just providing internet access.

"Our approach can estimate the number of people walking in an area, based on only the received power measurements of a Wi-Fi link," said Yasamin Mostofi, professor of electrical and computer engineering.

This approach does not require people to carry Wi-Fi-enabled devices for them to be counted.

To accomplish this feat of people-counting, the researchers put two Wi-Fi cards at opposite ends of a target area.

Using only the received power measurements of the link between the two cards, their approach can estimate the number of people walking in that area.

So far, they have successfully tested with up to nine people, including in both indoor and outdoor settings.

The presence of people attenuates the signal in the direct line of sight between the Wi-Fi cards if a person crosses the line of sight.

Human bodies also scatter the signal -- resulting in a phenomenon called multi-path fading -- when they are not in the direct line of sight path.

By developing a probabilistic mathematical framework based on these two key phenomena, the researchers have then proposed a way of estimating the number of people walking in the space.

The ability to estimate the number of people in a given space could be used in smart homes and buildings, so air conditioning and heating could be adjusted according to the level of occupancy.

"Stores can benefit from counting the number of shoppers for better business planning," said Mostofi.

Security and search-and-rescue operations could also take advantage of occupancy estimation.

The findings are forthcoming in the Institute of Electrical and Electronics Engineers Journal.