With Rear Window’s (1954) set being one enormous construct, Hitchcock needed a way to communicate stage direction to all the actors without being in their presence. Since most of the film’s camera shots originate from Jeff’s (James Stewart) apartment, Hitchcock spent the majority of his directorial time in that unit. The film’s massive lighting control units were also in the apartment, so it served as the base of operation for the rest of the production.

To achieve the direction of actors in scattered locations around the set, each character wore a flesh-colored earpiece so Hitchcock and members of production could communicate stage directions from Jeff’s apartment.

“Hitchcock could speak into the short-wave radio and direct the actors’ pantomime by giving cues as they performed, much like silent film direction.” - Scott Curtis, Alfred Hitchcock’s Rear Window