Not for the first time, a company has developed what it says is a paint that, when applied to walls, will block out (or, more importantly, keep in) radio signals like those used by Wi-Fi.
EM-SEC Technologies of Hampton, Virginia says its EM-SEC Coating System (PDF) is an "electromagnetic barrier for the containment of wireless networks" that "reduces the threat from electronic eavesdropping and blocks out electromagnetic interference for the protection of electronic data," according to a statement quoting Robert Boyd, vice president and director of technology at the company.
The "paint" is a water-based shielding developed for the U.S. government and military -- it is approved as a TEMPEST (Telecommunications Electronics Material Protected from Emanating Spurious Transmissions) countermeasure by the National Security Agency (NSA). EM-SEC plans now to sell it to the private sector. No word on the cost.
This isn't the first radio-resistant paint or wall covering to come out. In 2004, a company named Force Field Wireless began selling DefendAir Radio Shield, a flat interior paint that it says reduces transmission of signals running at 5GHz or less. They sell it by the gallon, by the quart, and as an additive for other kinds of paint. They also sell a Windows Shield film that they say stops radio waves below 4GHz. (The Force Field Wireless online store appears to be defunct, however, at the time of this writing.)
Also in 2004, a British contractor named BAE Systems created a "stealthy wallpaper" called FSS (Frequency Selective Surface), made up of panels similar to circuit boards, which can block some signals and let others in.