Force Field Door
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 MCM. 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 up. 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.
- 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.
- 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.
- And they do apparently have physical doors as a backup: a Trade Federation battleship gets its shield generators blown up, and immediately closes physical doors over the hangar.
- Titan A.E.: Cale is thrown into one of these energy jails by the Dredj. Seemingly inescapable, his only hope is to touch the walls, using his fingers force himself out of the cell.
- The cell doors in Tron are beams of energy. Admittedly, they are already in the internet and everything is energy, but there are still solid objects.
- 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.
- In Star Trek Generations, Soran protected his missile launch site with a massive force field wall. Unfortunately, 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.
- In Stargate Atlantis the titular city had holding cells with energy shields covering actual bars. The Ancients weren't that self-confident.
- Whoever designed the brig must have suffered from some kind of acute practicality syndrome, because the Ancients really are that self-confident. Case in point, a force field is the only thing holding the air inside Atlantis when it's in space.
- Atlantis also has one built into its Stargate, serving the same function as the Iris on Earth's Stargate.
- Stargate SG-1 once featured an interesting variant—a prison cell that used the force of gravity as its "Force Field Door". The cell was a long corridor with a dead end hooked up to an Artificial Gravity generator. When this was turned on, the end of the corridor became 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" became a corridor again, and guards could walk in or out. The resulting perspective shifts allowed for nice little Camera Tricks. The flaw was the same as that of any Force Field Door: cut the power, and the prisoner can simply walk out.
- They should have built the cell as a pit, and used the artificial gravity generator to get in and out. Or a ladder.
- One Star Trek: The Next Generation episode "We'll Always Have Paris" had the bar variant in Dr. Manheim's lab.
- Cell doors in Star Trek: The Next Generation and Deep Space Nine were energy fields.
- Add Star Trek: The Original Series, e.g. "Assignment Earth".
- Star Trek: Voyager (in general a frequent offender with this trope) actually had an episode in which Voyager was 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 had Force Field Doors. Predictably, a Standard Starship Scuffle ensued, and, lo and behold, the very first victim of Subsystem Damage was the cargo bay's power... The Oh Crap expressions on the bridge crew's faces when they learned of this were 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, was the exception and had a good old-fashioned solid door for their brig, made out of some reinforced transparent material. It seemed 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.
- 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.
- 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 tropes (and trains)though while preventing Gordon and his rebel friends access.
- In Metroid, 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.
- In Knights of the Old Republic 2, the Exile, Atton, and Kreia find themselves in force cages repeatedly, which Atton lampshades.
- 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 in one of these cells and then have a power outage, as jedi can jump that high.
- Common in the Ratchet and 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.
- 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 on a Prison Ship.
- It seems like every alien base in Subnautica has at least one doorway blocked by a forcefield, requiring you to find a "tablet" of the appropriate color to open it.
- 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. He fabricates a glass of water and shorts out the door. You can see it here.
- 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.