A standard way to bar entry or exit for characters in Speculative Fiction is to use a Force Field Door. It may be made of Some Kind of Force Field, glowing bars of Pure Energy, concentric Instant Runes, or what have you. If touched, it may harmlessly shock or dematerialize the appendage doing the touching. Sometimes, especially if the field is invisible until touched, it leads to amusing situations where characters run face first into the field.
Aside from Rule of Cool, the advantage of such a setup is usually that it is immune to physical attack, or that it can contain Starfish Aliens that could phase or shape-shift their way through ordinary doors.
Of course, the flaw in this immaterial marvel is it usually requires an outside energy source, or can be interfered with by using powerful ECM or MCMnote . So the hero can traipse past these obstacles by pulling the proverbial plug on it. Worse is when the outside energy source is on the outside of the Force Field Door, making disabling it as easy as beating up some guards and blowing it upnote . Or blowing a hole in the wall on the side, whichever is easiest. For some reason, the jailers rarely use physical doors outside the field (or wrapped in the field) as a backup in case of power failure.
If the force field door is on every side of a room, then it's like a Force Field Cage, which redirects to this trope.
There is a small amount of justification in this trope. Force field doors are very easy to use when you actually want to release someone at some point. Regular doors are just as vulnerable to blowing a hole in the side of the room. Having a system that fails open or fails closed is very much dependent on what you want the system to do.
- In Legionnaires #22, the Planet Hell prison has force field doors on the cells. When the Legion and Workforce get locked up by the escaped prisoners, Karate Kid is able to find a weak point in the field, which shorts it out when struck.
- Monsters vs. Aliens: Gallaxhar puts Ginormica in a force field cage... which she then tears apart with her bare hands! Makes sense, as she is full of Unobtainium, which is more powerful than anything Gallaxhar has.
- Titan A.E.: Cale is thrown into one of these energy jails by the Drej (whose use of them is Justified: everything they build is made of force fields). It seems inescapable, until Cale realizes that the Drej phase through their own energy barriers all the time, and manages to work out how to do it himself.
- Likewise, the cell blocks in Final Fantasy: The Spirits Within. So naturally, when the city's power grid goes down, so do the "bars" in the cells.
- Nightlife, a 1980s vampire TV movie starring Mirriam D'abo and Ben Cross, featured a doctor jury rigging a prison cell for a vampire by hanging ultraviolet lamps above the only doorway into a room, as well as on the ceiling a few feet down the hall in either direction. If the vampire crossed the beam, he burst into flames. See it here.
- Star Wars had several, most notably the barrier that forces Obi-Wan and Darth Maul to wait momentarily before their battle. Just about every large starship in Star Wars has some part of the hull, usually a hangar, that's open to the vacuum of space. How do crew members breath and not get sucked out into the void? Force fields. Seen in Episode III when Anakin blasts the force field generator over a Separatist battleship's hangar bay and air starts rushing out until a physical door closes over it.
- The cell doors in TRON are beams of energy. Admittedly, they are already in the computer system and everything is energy, but there are still solid objects.
- In Star Trek: Generations, Soran protected his missile launch site with a massive force field wall. Fortunately, it didn't penetrate the ground, which allowed Picard to bypass it through a tight rock arch it happened to rest on. Also an inversion, as Soran is the one inside the force field.
- Star Trek V: The Final Frontier deserves special mention. When Kirk and company are held in their own brig, complete with force-field door, they hear tapping on the rear wall. They slowly piece out the Morse Code message: "Stand back". Which they do just before their ally renders the force field moot with high explosives.
- Stargate Atlantis:
- Atlantis has one built into its Stargate, serving the same function as the Iris on Earth's Stargate, with the extra advantage that it can't be overheated by firing exotic weapons through the Stargate (something Earth's Iris has had to deal with).
- The city also has holding cells with energy shields covering actual bars. Surprising coming from the Ancients, who were usually very self-confident (case in point, a force field is the only thing holding the air inside Atlantis when it's in space).
- Stargate SG-1 once features an interesting variant — a prison cell that uses the force of gravity as its "Force-Field Door". The cell is a long corridor with a dead end hooked up to an Artificial Gravity generator. When this is turned on, the end of the corridor becomes the floor of a deep pit, thus preventing escape for anyone inside (and ensuring a painful landing for an unprepared prisoner). When turned off, the "pit" becomes a corridor again, and guards can walk in or out. The resulting perspective shifts allowed for nice little Camera Tricks. The flaw is the same as that of any Force-Field Door: cut the power, and the prisoner can simply walk out.
- Star Trek:
- Cell doors in Star Trek: The Next Generation and Deep Space Nine are energy fields.
- One Star Trek: The Next Generation episode "We'll Always Have Paris" had the bar variant in Dr. Manheim's lab.
- Odo from Deep Space Nine had to be held in a room surrounded entirely with force fields, to keep him from escaping in his liquid form.
- Add Star Trek: The Original Series, e.g. "Assignment Earth".
- Star Trek: Voyager (in general a frequent offender with this trope) actually has an episode in which Voyager is temporarily converted into a Prison Ship, transporting a large number of dangerous alien prisoners in a converted cargo bay. Of course, all the cells added to the bay have Force-Field Doors. Predictably, a Standard Starship Scuffle ensues, and, lo and behold, the very first victim of Subsystem Damage is the cargo bay's power... The Oh, Crap! expressions on the bridge crew's faces when they learn of this are priceless. "Oh, woe, if only there was some other way we could have locked up those prisoners!"
- Star Trek: Enterprise, being set in the 'verse's past, is the exception and has a good old-fashioned solid door for their brig, made out of some reinforced transparent material. It seems to work just as well as the force-field doors on all the later Enterprises...
- In the Firefly episode The Train Job, in the intro, Mal is thrown through what is evidently a force-field window: it vanishes as he passes through it, before reappearing a moment later. Assuming it performs the actual function of a window (keeping outside air out, and inside air in), it's most certainly an example of this trope, but they're never seen again.
- In Agents of S.H.I.E.L.D., Skye has to visit a Boxed Crook (former agent Grant Ward) in a cell with one of these. It can go opaque or soundproof at the push of a button. Skye Lampshades one of the problems with this trope when she makes absolutely sure that there's no button she can push to accidentally turn it off.
- Space: 1999. The episode "The Metamorph" has a classic Force-Field Door for the prison cell on the planet Psychon. Normally invisible, it emits a brief flash that stun the prisoners when touched.
- Blake's 7. In "City At The Edge Of The World", the Villain of the Week forces Vila to break through a door to a vault that he's convinced has enormous wealth. Vila works out that the door is actually a disguised forcefield — any force used against it only reflects back at the attacker (the villain gets his just deserts when he tries blasting through with a laser cannon). Meanwhile Vila and the Girl of the Week have gotten into the vault, only to finds it's a long-range teleporter to a distant spacecraft, where they'll live only as long as the oxygen that was transported with them lasts. When they don't die of asphyxiation, Vila has a Eureka Moment that the spacecraft has reached its destination, and the wall is another disguised forcefield door with the air seeping in from the outside world.
- Dungeons & Dragons:
- Adventure S3 Expedition to the Barrier Peaks. The spaceship's police headquarters had cells with 3 normal walls and one force field wall.
- D&D in general likes its magical force wall/cage effects. Depending on the edition, though, this can be justified in that those don't actually depend on an external power source and can be effectively indestructible if the exact right countermeasures aren't at hand, making permanent versions potentially actually superior to mundane physical barriers.
- These appear in Batman: Arkham Asylum. They must be turned off before Bats can go further.
- These show up occasionally in the Crash Bandicoot series of games. Typically in the Warp Rooms, barring off access to later chambers until you clear the one before it.
- In Half-Life 2 some of the obstacles included energy fields to which you needed to shut off the power to get past. Often by literally pulling out a (inexplicably large) wall plug. These fields also allow combine troops (and trains) though while preventing Gordon and his rebel friends access.
- In Metroid games, doors are, with one exception, surrounded by force fields. These are always Color-Coded for Your Convenience and thus a Broken Bridge till you collect the right upgrade. The Prime series actually justifies the door-shields: the door were set up to separate distinct areas from each other. The doors are actually motion-activated, opening when a sufficiently large life-form approaches it, but to prevent the doors opening and closing ceaselessly for the indigenous life, the force-field was set up, which could only be deactivated by an energy weapon from a sufficiently advanced species. It wasn't so much to keep people in and out of certain areas (though that's inevitably what they do...to Samus), but rather to prevent wear and tear from constantly opening and closing.
- Knights of the Old Republic:
- In Knights of the Old Republic 2, the Exile, Atton, and Kreia find themselves in force cages repeatedly, which Atton lampshades. The fields cause "only mild electrical burns" when touched.
- Both games feature quite a few force field cages and doors. Some of these require you have certain members in your party before you can pass through them (e.g Jolee to get down to the Lower Shadowlands on Kashyyyk).
- In Raidou Kuzunoha vs. King Abaddon Dahn and his rogue Fukoshi are imprisoned in one. The "forcefield" can't be seen through, but the unoccupied cells in the same room have backup bars. (The forcefield is in place to block their insect summoning whistles.)
- In Jedi Knight: Jedi Academy, one mission involves escaping from a prison where an enemy has thrown Jayden. Each prison cell has four walls but no doors. The ceiling is a force field. Smart design, considering most people can't jump that high. Not smart when you put a Jedi (who can jump that high) in one of these cells and then let him out to play the most dangerous game with him.
- Common in the Ratchet & Clank series. Sometimes Ratchet (or Clank) has to step on a button to open them, sometimes he has to trick or persuade some other character to step on the button, and sometimes he has to destroy the mechanism.
- The Fallout series has multiple kinds of forcefields.
- Shows up a lot in the modern Sonic the Hedgehog games. They usually require you to flip a switch or destroy an encounter's worth of enemies to drop them. Other puzzles revolve around activating these to use as a walkway and sometimes even navigating mazes made entirely of them.
- In Superhero League of Hoboken, Dr Entropy protects his first dastardly device behind a force field... but while the generator is placed on the inside, its power cord is plugged into an outlet on the outside, allowing the heroes to disable the field with one swift pull.
- In the Perpetual Testing Initiative for Portal 2, an alternate Cave Johnson learns the hard way why these things are bad idea on a Prison Ship — especially when you consider power outages.
Cave: Man, those blue force fields looked good, though. Every time I saw one, I thought, "Wow! I am in space." Still, though... A door made out of paper would have been better in the long run. Would have at least slowed 'em down for a second.
- Unreal I has them all over, as well the consequences of turning off the power...
- Warframe features these heavily on both Corpus and Grineer ships. The former will deplete your shields, and fling you away from the door, as if you were struck by a shockwave, and need to be disabled by shooting (or staying out of sight of) security cameras, and the latter will proc Magnetic damage on you, draining all of your shields and energy, and are disabled by shooting ID scanner over the doorframe.
- Dishonored has force fields (called Walls of Light) that zap to ash anyone/thing unauthorized that tries to go through them. There are plenty of ways to circumvent them, however; there's usually an alternate entrance, you can remove the power source, you can rewire them to let you through and obliterate guards, and you can just throw stuff through the field until it runs out of power. One particular odd form of the latter is summoning a swarm of rats and guiding them into the wall. Two expensive ways to get through them involve Demonic Possession of a guard who is authorized and hop across that way, and the other is to use the advanced version of Bend Time to literally stop time and cross without fear of being zapped.
- In Arcanum, Arronax was captured by Big Bad and kept in a magical force field capsule barely lagrer than his body for two thousand years.
- A standard in Warcraft III, turning these off is often a matter of killing the generator of boss powering them.
- PlanetSide 2 uses forcefields in lieu of doors. Every base has impenetrable shields around the spawn building; at large facilities, these can be taken out by blowing up the generator that powers the spawn tubes. Other uses of shields are to protect vehicle garages — which often have the generator on the outside - or to delay attackers from capturing the base's control point. Planetside 1 used far more reasonable physical doors for pretty much every situation, only using force fields doors for the vehicle gateways in facility walls.
- The Castles of Doctor Creep has the Force Field as one of the many obstacles you face. It is impossble to move through a force field (your character will stop just short of touching it), but on the flip side it will block a shot from the Ray Gun. By default, all force fields are on; the only way to shut a force field off is to press a corresponding button. However, the button will only shut the force field off for eight seconds; once time is up, the force field(s) that the button shut off will reactivate.
- XCOM: Enemy Unknown has the aliens use force-fields for their doors and protection for their Elerium engines which the Humans incorporate into their own design.
- Dark Souls features magic barriers that bar the Chosen Undead from entering the Duke's Archives, the lower section of the Tomb of the Giants and the section of the Demon Ruins just before Lost Izalith until they acquire the Lordvessel and place it at Firelink Altar. Similar barriers will also serve to isolate a character within a certain area if they're being invaded or have entered another player's world.
- The Talos Principle: Most puzzles feature at least one of these. They appear as blue barriers and can be deactivated pointing a jammer at them, putting some weight on a nearby pressure switch, or pointing a laser of the appropriate color into a nearby receiver.
- Quentyn Quinn, Space Ranger (an IN SPACE! spinoff from Tales of the Questor):
- During an arc skewering Star Trek, the main character is placed in a cell guarded by a force field and discovers he's been furnished with a replicator that can produce any food or drink he wishes. (Something the actual Trek examples didn't have, by the by.) He fabricates a glass of water and shorts out the door. You can see it here.
- Earlier, they entered the shuttle bay through a force field, much to Omnibus's exasperation.
- In El Goonish Shive, Raven considers it "standard lockdown procedure" to put up force fields sealing off all the doors and some of the hallways when his school is under a magical threat. Not that it stops Abraham, however.
- The supervillain prisons in The Avengers: Earth's Mightiest Heroes! use this kind of door.
- In the DuckTales (1987) episode "Armstrong", Armstrong sticks Scrooge and Gyro in a closet, behind a force field.
- Kaeloo: In Episode 105, the door leading to the magical staircase is a force field door. Only the Pure of Heart may pass through it; anyone who isn't pure gets an electric shock.
- The cells on Peridot's ships in Steven Universe are of this kind, and they temporarily vaporize Ruby's hand when she touches it. Only one thing they didn't account on — the cells are only designed to hold the projected Gem bodies. Steven's organic form had no problem walking straight through and can block the field projector to let his friends out.
- Plasma window. No, really.
- Considering that atoms are mostly empty space, and only feel solid due to the strong negative charge present on their surface (such that it is) which repels other atoms in a similar manner to what happens when you try to touch the south poles of two magnets together, ordinary doors are technically examples of this trope. Subverted in that you're just as much force-field as they.