The Conversation (1974)

Harry Caul (Gene Hackman) is a professional surveillance expert who has been hired by “the director” of some nameless organization to record the private conversation of a young man and woman in San Francisco’s Union Square.

In the course of listening to the conversation, Harry begins to believe the couple is in danger, a feeling exacerbated by his guilt over three deaths that were a result of information he provided. Harry’s misgivings seem to be confirmed when he has a nasty confrontation with Martin Stett (Harrison Ford), an assistant to the director.

Harry then attends a convention of surveillance experts and security technicians in the St. Francis Hotel. Aisles of exhibit booths advertise the latest security, enforcement, communication, and detection devices. One enthusiastic marketer hawks the latest LT 500 model: “This Is the One That Does It All!” While inspecting a video system, Harry sees Martin Stett on the video screen, and later encounters him in the hotel. The spy is being spied upon.