Source: Telegraph
The researchers say that the variation of radio signals in a wireless network can reveal the movements of people behind closed doors or even a wall.
Joey Wilson and Neal Patwari, from the University of Utah, have used the principle of variance-based radio tomographic imaging. The system works by measuring interference between the nodes of wireless devices. If someone passes through that field, the device registers a change in the levels of resistance, and feeds that information back to a computer.
The system can currently only see about three feet through a wall, and is so far only capable of sensing motion. At this stage, it is not sophisticated enough to generate an actual image of what lies beyond the wall, but the research team is confident that this feature could be developed in time.
The researchers said the technology could be used in search and rescue operations, with emergency teams using the same radio technology used by Wi-Fi networks to build a web of sensors around a disaster site, revealing the location of victims and survivors.
"We envision a building imaging scenario similar to the following. Emergency responders, military forces, or police arrive at a scene where entry into a building is potentially dangerous. They deploy radio sensors around (and potentially on top of) the building area, either by throwing or launching them, or dropping them while moving around the building," wrote Wilson and Patwari on the arXiv science forum.
"The nodes immediately form a network and self-localise, perhaps using information about the size and shape of the building from a database (eg Google maps) and some known-location coordinates (eg using GPS). Then, nodes begin to transmit, making signal strength measurements on links which cross the building or area of interest. The received signal strength measurements of each link are transmitted back to a base station and used to estimate the positions of moving people and objects within the building." | 
