Shock Collar

The concept of a Shock Collar is simple: A character is forced to wear a Slave Collar or torc and when he does something undesirable, as designated by whoever put the collar on him, he is shocked. Such things exist in real life for dogs but it is more likely that the trope is in use as a way to replicate the iron slave collar with a Speculative Fiction twist.

How it actually works is nearly always undefined. It's a metal ring, it hurts, end of. Sometimes it is electricity for some Electric Torture, sometimes it's a generic Agony Beam generated by some alien Techno Babble. It makes a good Restraining Bolt for the plot, you can even spin some plot lines out of how to get it off, and sometimes it'll have the added feature of being able to be pumped up to deadly levels so that it can also be, effectively, an Explosive Leash. On other occasions expect some fun with Pavlovian conditioning.

Anime & Manga

 * This happened in Mahou Sensei Negima to the girls under slavery in the magical world.
 * In Slayers captured Lina Inverse was restrained by a circlet that zapped her when she tried to use magic. They really haven't a slightest idea what her big sister used to put her through, however...
 * Inuyasha has a collar of enchanted prayer beads (or rosary) designed to make him hit the ground whenever Kagome says "Osuwari" or "Sit" / "Sit, boy". Kagome is an easily pissed off Tsundere Type B. Bad day for Inuyasha.
 * Boys Love Genre Ai no Kusabi's plot revolves around how Badass Biker Riki was made into a Sex Slave by Iason Mink. Each "Pet" gets an identity ring in the standard form of jewelry like earrings, necklaces and such. Iason uniquely makes Riki's a cock ring which doubles as a Restraining Bolt Shock Collar whenever Riki rebels. Which is often.

Comic Books

 * The more villainous members of DC's Suicide Squad were fitted with these on missions. If they got too out of line, the collar could also be commanded to blow off their heads.
 * 1980's British Starblazer.
 * The Slave Collar had variable pain settings to punish wearers who disobeyed their owner.
 * Issue 157 "Warworld", The Valk put headbands on their prisoners that can inflict any level of pain on their victims, up to and including death.

Film

 * In Coneheads, the two humans are carted off to the Conehead homeworld and kept in check by a collar with glowy red lights.
 * The eponymous hero wears one in Hell Comes to Frogtown.
 * Cartman has a microchip implanted in his skull in South Park: Bigger, Longer & Uncut. It sends out an electric jolt when he swears, in an effort to make him stop swearing. It, for the most part, doesn't work; towards the end of the movie it even turns into a Deus Ex Machina.
 * In the 1996 version of The Island of Doctor Moreau, all of the beast-folk have an implant that causes them excruciating pain when a remote control is triggered. This system of keeping them in check backfires when the Hyena-Swine figures this out and removes his own implant, then steals the control device to use it to dominate the others.
 * In Crank 2: High Voltage, Chev Chelios encounters two assholes that are torturing a dog with a shock collar even though it was obeying their commands. Chev tells them off, takes the collar, and puts it on. They try to shock him, but the electricity just powers up his artificial heart.

Literature

 * In Harry Harrison's The Stainless Steel Rat's Revenge, the Grey Men attach one to James ("Slippery Jim") diGriz, connected by a cable to a control box. It inflicts searing pain by stimulating neurons in the brain.
 * Han Solo's Revenge: The Lurrian slaves captured by Magg and Zlarb are chained together, the collars acting as Shock Collars: the slavers can hit the whole string at once in an emergency.
 * Jim Butcher's Codex Alera has slave collars that will hurt the slave if they disobey or go against the master's will (to the extent that calling the person "bad" for no reason will hurt them) and send signals of pleasure when the person obeys. They often drive the victim completely insane, and it's played for every possible drop of horror.
 * A similar device is used in Parable of the Sower and its sequel, by slavers to keep their slaves in line. Lauren and her community also have these put on them when they are attacked and captured in the second book.
 * Voluntary example: In the Dream Park series, Gamers wear remote-control amulets that deliver a mild electrical stimulus to inform them that they've been killed out of a scenario. The initial shock is merely uncomfortable, but if a player stubbornly refuses to lie down and "die" when the simulation demands it, the voltage can be increased to inflict actual pain. (Presumably they're required to sign a release to allow this.)
 * In the third book of the Soul Rider series by Jack Chalker, a captive Cassie receives a shock collar to assist in her re-education by New Eden

Live Action TV

 * Babylon 5
 * When the captain of Babylon Five, John Sheridan, found himself captured by the Earth government, who had recently given themselves a little 1984 Shout-Out by setting up the Ministry of Peace, he had a Shock Collar put in place as a Restraining Bolt to explain why he didn't just attack the torturer who was trying to make him see four lights sign a confession.
 * A torturer/assassin makes G'Kar wear one. One of his political enemies on the Kah'Ree had just died, and wished to exact revenge.
 * Star Trek: The Original Series had two episodes with collars that inflicted pain:
 * "The Gamesters of Triskelion": Used by the title characters on their thralls.
 * "Spock's Brain": Belts used by the Eymorg women on their male slaves and the captured Enterprise crew members.
 * Both Twin Peaks and Cheers used the gag in which the wearer of the collar gets hold of its control box and uses it in the mistaken belief that it will shock the other person instead of himself.
 * Chiana is wearing one of these when she first appears on Farscape, activated by a button on her handler's forehead. In another episode, the entire crew is fitted with collars- even Pilot.
 * In an episode of Married... with Children, Al Bundy had to wear one.
 * These collars are worn by the imprisoned women in the "Gladiatrix" episode of Birds of Prey. It also drugged them to the point of insanity.
 * The aliens in The Outer Limits episode "Rite Of Passage" put shock wristbands on the humans they were raising to prevent them from trying to leave their enclosure. It wasn't due to malice; the woods were full of dangerous creatures.
 * Human slaves in Pylea wear these on Angel.

Newspaper Comics

 * In one Zits comic, Jeremy's mother forces him to wear a shock collar to stay at home after he breaks curfew one time too many.
 * There was a series of Dilbert strips where the employees all had to wear headbands that the boss could use to shock them at will. Dilbert reprogrammed his to redirect its signal to Wally.

Tabletop Games

 * Caverns of the Snow Witch, one of the Fighting Fantasy gamebooks, has the Snow Witch fit collars onto her slaves, so that when they disobey her orders, they get choked.
 * Rogue Trader has shock collar that helps with using Wrangling skill - but if such a test is failed too badly, the creature is enraged and attacks.

Video Games

 * In a case of Shock Collars being used for good, in Batman: Arkham Asylum the inmates have shock collars (dubbed "Suicide Collars") that double as life sign monitors. We see them demonstrated at the beginning as the only thing that can help keep Killer Croc under control in a Chekhov's Gun moment.
 * A bit more of a straight use of this trope occurs in the game as well, since The Joker uses them to keep tabs on his goons (and as an alert system to where Batman is or has been) and presumably also uses them when they get too out of line. Batman can also overload the collars with a specialized batarang so that they shock the goon wearing it into unconsciousness.
 * In Mother 3, Salsa the monkey has a Shock Collar that is used by Fassad to punish him.
 * The Kingdom of Loathing Web Game has the Stab Bat, a familiar with the unfortunate habit of stabbing the player rather than the enemy every now and then. The familiar-specific equipment is, appropriately enough, a Shock Collar.
 * Dungeon Siege II had your character wearing one near the start, after being captured by dryads.
 * Baldur's Gate II has one trippy level where you follow a band of kidnapped actors into a Pocket Dimension where the slaves are kept in line by a magical version of these collars. If you're schmuck enough to fall for the bait, you can pick them up and try them on.
 * In Star Wars: The Old Republic, slave girl Vette has one that the Sith Warrior can choose to abuse. However, you can also remove it for Video Game Caring Potential.

Webcomics

 * Freefall has the last surviving uplifted chimp wearing one, to facilitate relatively safe communication, since he's prone to rages. He keeps spare transponders for it to give the visitors not already wearing one (it's activated by approaching too close) and can switch it on and off himself - when going berserk, he becomes too stupid to just turn it off.

Western Animation

 * In Futurama's third movie, Bender's Game, Leela gets a shock collar to condition her to give up violence and profanity and all that other fun stuff.
 * In one episode of The Angry Beavers, the beavers are mistaken for dogs by a suburban family that gives them shock collars to housebreak them. "Bad puppies! We love you!"
 * Worn by Shego's subjects in her future dystopia in Kim Possible: A Sitch in Time.
 * The Simpsons: Sideshow Bob has a something similar, a Shock Bracelet Restraining Bolt, so the Simpsons can keep him under control as he was recruited by the police to uncover who is trying to kill Homer Simpson.
 * In the Fairly Oddparents episode "Wish Fixers", the Pixies make Timmy sign a contract that would supposedly help him get rid of any "bad" wishes and put collars on Cosmo and Wanda that release an electric shock every time they grant a wish that is considered "bad". In fact, the only good wish on the contract is handing Fairy World over to the Pixies. However, thanks to a loophole in the contract (making an irresponsible wish that is at the same time responsible will cause the contract to be null and void), Timmy wishes for both his godparents to be made of rubber, making them immune to the shocks and nullifying the contract as a result.