Probably the most boring of the interfaces in the story (from an interaction design perspective, rather than an ethical one), these are monochrome monitors showing feeds from hidden, closed-circuit television cameras in places around the castle—including places you’d expect to be private.

Magenta and Riff Raff watch Janet’s bedroom from the laboratory.

Magenta and Columbia watch the laboratory feed from a castle room.

Riff Raff lets Frank-N-Furter know that Rocky has escaped via the monitor in Brad’s room.

Dr. Scott appears at the front of the castle as seen from the laboratory monitor.

The monitors are unusual for being octagonal, but this looks like a frame on a 4:3 television, standard for the mid-1970s. Note that the show that made this treatment much more famous was Battlestar Galactica, which would air 3 years after this movie’s release. (Another potential influence?)

Interfaces

Magenta and Columbia’s monitor has a single dial in the upper right. We never see it in use.

The one interface we see in use on any of the monitors is the arm to the right of the one in the laboratory. It reminds of me of a slot machine arm, but when we see Janet and Riff Raff operate it, they manually pull and return it to the upright position. So it lacks the spring-return behavior of slot machine arms. No, it seems to be a positional lever, and the raised and lowered positions do…something…but it’s unclear what.

Such arms would most befit two states, because the extents of the range are easy for a user to achieve. But there are more than two states.

How do they turn it off and on? (We see the laboratory monitor off and on.) How do they change the channel to view other feeds? (The laboratory monitor shows both Janet’s bedroom and the front door feed.) How do they control the volume?

Then if we were to think of these things for general use: How do they turn off the cameras for privacy?

Could we backworld it?

Yes, it’s possible that the arm position is not binary up-or-down but continuous, with angles defined as having meaning, and timing helping set the boundaries of input. Like, pull it 3° and hold for a second and that puts the system in the select-new-channel state. Or maybe each of the Transsexual keyboard keys is mapped to individual angles, like A = 85–90°, B = 80–84°, and so on. The user would have to move it to the right angle and hold it there for a second for that character to be sent to the processor before returning it to 90° as an “ENTER” function. This has historical precedent in the Quadrant telegraph by Louis Francois Clement Breguet in the mid-1800s. Pictured below is the sending mechanism for such a system.

Quadrant telegraph by Louis Francois Clement Breguet

But note that the usability here is provided by a printed guide below the lever that shows what regions map to what letters, so it’s easy to position and confirm that the arm is in the right spot before pressing the commit control. It would be a terrible experience to try and use this without guides or feedback. It would require too much precision and be very error prone. I can’t backworld this into any semblance of sense or usability. Especially since Janet seems to have no problem using it when she encounters the device.

Before anyone comes at me with, “Maybe Transsexuals have more precision and memory and…”, remember we design for humans, and must evaluate interfaces from that POV.

There is an odd moment when Dr. Scott first appears on the laboratory monitor. The shot is close up on the monitor, so it’s hard to tell if it was due to some action a character took, but the screen goes from staticky to the correct channel showing Dr. Scott. Many modern systems do that—think of how Zoom automatically switches to the camera showing the current speaker—but it would take a vigilant person doing technical direction back in 1975. I’m unprepared to ascribe context awareness to the design of these interfaces, but it would be way ahead of its time if it did. After the close-up shot, a pulled back shot shows Riff Raff returning the lever to vertical. This implies he was there off camera pulling the lever in the first shot, but the film does not show what signal might have had him reaching for it in the first place, or what he did to select the channel where Dr. Scott was shown.

So, in the end, the monitors are a narrative interface, conveying the voyeurism and communication plot moments. Their interfaces are handwaves that enable “character sees thing” beats, and we have to leave them as such.

IMDB: https://www.imdb.com/title/tt0073629/Currently streaming on: