TEMPEST

Your screen broadcasts itself; a van outside can read it. Classified for decades under a name that is itself classified.

TEMPEST: the NSA codename for the discipline of intercepting information from unintentional emanations — electromagnetic leakage from screens, cables, and keyboards. Documented: declassified NSA history ('TEMPEST: A Signal Problem') traces discovery to a WWII Bell Labs teletype finding; van Eck's 1985 open paper demonstrated reconstructing CRT screens at a distance with cheap equipment; shielding standards (SDIP-27) govern secure facilities today. The proven physics floor under surveillance lore: the walls really can hear, in a documented, engineering-manual sense.