The F.C.C. regulates the airwaves in the U.S.A. Here is their official line on jamming: The operation of transmitters designed to jam or block wireless communications is a violation of the Communications Act of 1934, as amended (“Act”). See 47 U.S.C. Sections 301, 302a, 333. The Act prohibits any person from willfully or maliciously interfering [...]

While the law clearly prohibits using a device to actively disrupt a cell-phone, bluetooth, or WiFi signal, there are no rules against passive blocking of necessary transmissions. That means using things like wallpaper or building materials embedded with metal fragments to prevent cell-phone or WiFi signals from reaching inside or outside the room. Some buildings [...]