According to Technology Review, it is now possible to see through walls using a wireless network. Neal Patwari and Joey Wilson, two researchers at the University of Utah tested and proved the idea using a wireless network with 34 nodes and the IEEE 802.4 wireless protocol.
The idea behind it all is that the signal strength varies as a person moves through the room, because it changes the distance of the paths the radio waves have to take to reach the receiver. By probing this space with signals that then get collected by receivers, forming a vision of what goes on inside the room.
The possibility of seeing behind closed doors is not a novelty, but what is interesting is that this solution is rather cheap and easy to implement. But, even if we can think of a hundred instances for good use of this technique (called variance-based radio tomographic imaging), there is still the possibility of it being used to harm people (for example, thieves seeing if the house is empty and, therefore, a good target), or at least, invade their privacy.