Researchers at the University of Utah have found a way to see through walls to detect movement inside a building.

The surveillance technique is called variance-based radio tomographic imaging and works by visualizing variations in radio waves as they travel to nodes in a wireless network. A person moving inside a building will cause the waves to vary in that location, the researchers found, allowing an observer to map their position.

The researchers, electrical engineering graduate student Joey Wilson and his faculty advisor Neil Patwari, have tested the technique with a 34-node wireless network using the IEEE 802.15.4 wireless protocol, according to the MIT Technology Review. By "interrogating" the space with signals and multiple receivers, the researchers found they were able to read the waves to detect the location of a moving object within a meter of accuracy.

The technique could be used by SWAT teams trying to determine the location of a sniper or hostages in a building or by first responders looking for signs of life in a building that is too dangerous to enter.

The responders could conceivably launch a series of radio sensors in the direction of a building, deploying them on each side and even on the roof, the researchers say. Once the nodes begin to transmit, the responders could measure the received signals as they're transmitted to a base station.

Of course there are privacy and security concerns associated with the technology. A burglar could use it to detect if anyone is home or to scout the location of security guards.