We've all seen automatic doors in Real Life - a person walks into range of the sensor and the door opens. As long as there is someone in the sensor's area the door stays open. Not in the future. There the doors only close if the characters are staying in the room, and if they're going straight out again, then the door conveniently stays open for them. They can have a chat where each person is on the opposite side of an open door, but as soon as the conversation is over, the door will close, without either person moving.
Also, when a person walks past a door with no intention of using it, the door will not open.
So, how do the doors know when to open? They must have read from the script.
Subtrope of Our Doors Are Different.
- Played with in Airplane II: The Sequel where the doors on the space station can only be opened and closed if you 'shh' at it.
- In one scene of Spaceballs, the sliding doors shut on Lord Helmet's helmet.
- The freezer that Eddie's trapped in in The Rocky Horror Picture Show opens for no reason so that Eddie can ride out on his motorcycle and sing Hot Patootie. Creator, Richard O'Brien notes this in the commentary and regrets not having Frank N. Furter accidentally hitting a button or something.
- In the original stage play, Columbia is shown accidentally opening the freezer door, and discovering Eddie.
- In The Hitchhiker's Guide to the Galaxy, the automatic doors on the Heart of Gold are characters in their own right. It is their pleasure to open for you and their satisfaction to close again with the knowledge of a job well done.
- Zaphod even tried to instruct a door how to open stealthily so he can get the jump on his unwanted boarders in one chapter of Life, the Universe and Everything. The door does exactly as he asks, then completely blows it by asking him - loudly - if that's what he wanted. Yes, the in-door voice has No Indoor Voice.
- In The Restaurant at the End of the Universe the elevators at the publishing office are precognitive so they know just when someone needs them. Unfortunately, they also refuse to bring passengers up to floors where they predict something bad is about to happen. They have therapists.
- Any amount of times on Star Trek. Oddly, the unaired Pilot "The Cage" has a door that opens when two characters walk into range, despite the fact that they were only running to get a view of the transporter.
- Particularly obvious in one episode of Star Trek: The Next Generation, when Picard makes a speech, and then walks towards the door. Then he pauses, right at the door, before turning back to give a final comment to cap his speech. The door doesn't open until it's quite sure he's finished.
- Another notable example: in "The Naked Time", Spock begins to feel the effects of a waterborne inhibition-removing chemical and ducks into an empty briefing room. As soon as he's out of sight, he slumps back against the doors, which fortunately stay closed.
- Lampshades in the Star Trek: Discovery episode, "The Red Angel" where Tilly apologizes for barging into a meeting, saying she should have knocked but couldn't because the doors open automatically.
- In a possible case of Reality Is Unrealistic, the TNG-era Star Trek production team once actually tried installing real automatic doors on the set rather than paying grips to pull back the prop doors. It didn't work because—yes—the doors opening and closing at "natural" times often spoiled dramatic moments in the script. There are outtakes where the grips missed their cue and the actors halt abruptly or walk into the doors.
- Possibly justified: The door sensors are likely monitored by the ship's computer, which would be sophisticated enough to read the body language of a moving person.
- In every incarnation of the Stargate franchise, the eponymous device is established to stay open for a maximum of thirty-eight minutes, but should supposedly shut down on its own when it's not being used. In practice, it knows to stay open until the characters go through, barring instances where the plot calls for it to stay up longer or for the cast to miss it. We've seen it stay open for ages for the sake of atmosphere, or close the instant the last character was through.
- This can be justified in any outgoing wormhole from Earth given there's a control room replacing the DHD who are presumably briefed on any outgoing traffic — almost literally making it a Script Reading Door. As for offworld-to-offworld wormholes or offworld-to-Earth wormholes, it might often be justified by a gate on the outgoing side of a wormhole detecting if all entities at the gate have or have not gone through the gate like any supermarket infrared or pressure-sensor door. Obviously some instances can't be justified even in this manner, however. For instance, when the burst of energy from the wormhole forming was used for a funeral offworld, the gate opened, vaporized the funeral pyre, then shut down instantly, as if aware it was being used for precisely that purpose. The guy operating the DHD didn't even touch it after activating it.
- Similarly, incoming visitors to Earth always step through after the iris is opened. This is justified for SG teams, since their GDOs relay an all-clear message, but at times there have been visitors possessing no such device yet managing the same.
- In one incident on Stargate Atlantis, one of the main characters has just had a heart-to-heart with his girlfriend, and as he walks away the door stays open just long enough for him to have a longing look back before closing despite being just outside the door (and therefore presumably still in the sensor's range). In another episode, the doors to the conference room close just in time to keep the last guy inside and they don't open when he steps back, then forward again.
- Mad TV: THE BLIND KUNG FU MASTA! was tripped up by the 'Star Trek doors' twice. First time it closed while he was still between the doors. The second time he was far enough away and the door closed, preventing anyone from hearing his speech (something about apples).
- In The Prisoner (1967), Number Six's front door seems to know when he's entering or leaving his home. Of course, he is living in a panopticon.
- In the Red Dwarf episode, Emohawk: Polymorph II, the airlock door starts to open as Ace Rimmer is reaching for the controls.
- When dragging a dead or unconscious body in Metal Gear Solid 3: Snake Eater, non-electronic doors will automatically swing open as you approach them and close behind you.
- Subverted in the first episode of Futurama, where they seem to be time based and when Fry spent too much time gawking at them, they closed on him, twice.
- This is averted and Played for Laughs on Star Trek: Lower Decks after Boimler returns from a stint on the Titan. He spends his return episode struggling with the doors because they're keyed to respond to individuals, not motion, and through a mishap Boimler's identity hasn't been properly logged (and he's too stubborn to just get it fixed). As a result, the doors keep slamming in his face or refusing to open.
- Averted on The Venture Bros.. When Brock is being treated in an OSI hospital level, an invisible man tries to escape and bounces off the doors, indicating that they use normal infrared sensors.
- Given the numerous breakthroughs made in human-robotics interfacing since the new millennium, most anticipatory door effects could be emulated (through rarely are) with contemporary smart-door technology.
- Person-sensors (motion, infrared, whatever) could track the trajectory of a moving person and only open if they would intersect the doorway.
- People interacting in a doorway face each other and express themselves, where people who are not interacting don't. A computer could easily interpret these behaviors.
- Identified persons (via ID transponders or biometrics) may be allowed through a door or barred from entering an area. Similarly, the door control system may know exactly where a specific person is going, and only open doors to and from that location.
- An idiosyncratic door system could be used to add an uncanny element (or sheer comedy) into a highly automated facility. Though this is rarely used or regarded in media.
- Some automatic doors stay in place with very little maintenance for several years. As a result, simply walking past won't always trigger the sensor. Other times, walking towards it won't trigger the sensor either and you'll end up walking into the door.