“Anti Wi-Fi Paint:

    The idea is simple: Use a special paint on walls where you don't want wireless to pass through (say the exterior of your house).  The secret is mixing aluminum-iron oxide particles in with the paint. The metal particles resonate at the same frequency as Wi-Fi and other radio waves, so signals can't pass through the thin layer of pigment. Outsiders would simply be unable to access your wireless network, just as you, inside the house, won't be able to interlope on anything beamed on the outside.

    The paint isn't just of interest to those concerned about wireless leaking out of the building. Movie theaters have long been interested in finding a legal way to keep cell phones silent during screenings. Electronic jammers that actively block wireless signals are illegal, but passive materials that prevent wireless signals from getting through are not. Since the wireless-blocking paint can also block the lower-frequency signals that cell phones use, addled mobile junkies would have no outlet for reaching the outside world.”

    -Yahoo Article, by Christopher Null   http://ca.tech.yahoo.com/computers/accessories/article/3904