How about a paint that will make a room secure against Wi-Fi? Basically, the idea would be to keep your Wi-Fi signals (think cell phone or wireless internet) from getting out where anyone could eavesdrop on them.
EM-SEC Technologies, a company in North Carolina, has developed the paint and has successfully tested it. I don’t have info on pricing, but it’s currently available and meets National Security Administration’s (NSA) TEMPEST (Telecommunications Electronics Material Protected from Emanating Spurious Transmissions) requirements. Since it’s intended for corporate and government security, my bet is that it’s pretty pricey.
However, the article where I originally saw this (afterdawn.com) suggested that it could be used to jam cell phone calls in a movie theater. Just put on fresh coat of paint!