A Faraday cage in a can!
Wireless networking is a neverending headache for system and network admins, and not just because some makes and models of access points are so flaky, the could have come out of a box of cereal. When you crank up an RF transceiver, the signals go everywhere, which means that people outside of a building can at least see some traffic beyond the walls, and sometimes beyond the property line. I don't think that I have to go into what a security threat this is... normally, you can use a Faraday cage to contain the signals, but building such a construction from scratch is not only expensive but prohibitive in complexity and PITA factor when you're talking about an entire building.
An outfit called EM-SEC Technologies has perfected a Faraday cage in a can, a metallic paint that blocks RF emissions in the part of the EM spectrum used by wi-fi devices. When securing a facility from wi-fi leakage, you just repaint the walls with this stuff and it helps mitigate the risk of someone cracking a network from the outside via a wireless access point, either one set up and administered by the organisation in question or a clandestinely installed AP.
Word has it that the US government has been using this stuff for a while, and they like it so much that EM-SEC Technologies has put it on the open market because it'll be profitable to sell it.