Commander Drury of the USIA (left) confers with Maxwell Smart in the "Hall of Hush".
Chamber at the United States Intelligence Agency devised by Dr. Denton where the spoken word is suppressed and replaced by visible airborne text as a means of thwarting would be eavesdroppers [TV Movie: "Get Smart, Again!"].
The Hall of Hush is essentially a high-tech version of the CONTROL Secret Word File, itself a replacement for the perennially-malfunctioning Cone of Silence [Episode #98: "Temporarily Out of CONTROL"].