IOWs a tinfoil hat.
Nay, say! Tempest testing, certification, and field compliance surveys are the real deal. Even in the 1970s they were able to reconstruct what was displayed on the screen of a CRT terminal from about a mile away. Compliance to Tempest meant that the equipment used for reception and transmission of classified information had to shielded according to standards and operated inside Faraday cages. ASR-33 teletypes were compliant while commercial grade CRTs were not.
One of my personal friends was an officer in the army in the 1980s; and, he got written up for using a commercial grade CRT in the signal center. He told me that the Tempest team entered the room and stated, "There is an unauthorized Hazeltine 1400 CRT in this room that is emitting classified information into the environment". They then laid screen-shots on a table which, sure enough, clearly exhibited information that was displayed on their CRT earlier in the day. The Tempest surveillance van was located off-post.
I had to use Tempest approved enclosures for computers on more than one government project.