DEC’s old offices here in the 1980s were paneled with drywall faced with copper foil, continuously grounded and taped with copper at all joints but painted over to look normal. And the windows had special coatings, too. It was supposedly a faraday cage, supposedly to stop van Eyck phreaking although it wasn’t called that yet.
The people who moved in a year or two after DEC left hated it! Used to complain all the time.
