We've all seen automatic doors in RealLife - 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.
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!!Examples

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[[folder:Films -- Live Action]]
* Played with in ''Film/AirplaneIITheSequel'' where the doors on the space station can only be opened and closed if you 'shh' at it.
* In one scene of ''Film/{{Spaceballs}}'', the sliding doors shut on Lord Helmet's helmet.
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[[folder:Literature]]
* In ''Franchise/TheHitchhikersGuideToTheGalaxy'', 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 ''Literature/LifeTheUniverseAndEverything''. 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 NoIndoorVoice.
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[[folder:Live Action TV]]
* Any amount of times on ''Franchise/StarTrek''. 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 ''Series/StarTrekTheNextGeneration'', when Picard makes a speech, and then walks towards the door. Then he pauses, right at the door, before he turning back and giving a final comment to cap his speech. The door doesn't open until it's quite sure he's finished.
** In a possible case of RealityIsUnrealistic, 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.
** Another notable example: in [[Series/StarTrekTheOriginalSeries "The Naked Time"]], Spock begins to feel the effects of [[EmotionBomb 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.
* In every incarnation of the ''Franchise/{{Stargate|Verse}}'' 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.
** 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 manage the same.
** In one incident on ''Series/StargateAtlantis'', 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.
* ''Series/MadTV'': ''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 ''ThePrisoner'', Number Six's front door seems to know when he's entering or leaving his home. Of course, he is living in a panopticon.
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[[folder:Western Animation]]
* 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.
* Averted on ''WesternAnimation/TheVentureBrothers''. 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.
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[[folder:Real Life]]
* 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 he or she 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 too 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.
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