Back before there were more technological means of detection and prevention, coal miners would iconically bring along canaries or other small birds with them as a form of early warning system to detect the presence of carbon monoxide. The bird's rapid breathing rate, small size, and high metabolism (compared to the miners) would result in them succumbing to poisonous gases before the miners, thereby giving them time to take action.
The Canary in a Coal Mine is a plot device used to detect danger. Historical works, period pieces, or fantasy settings that focus around mining might use the birds themselves, but the trope can be represented by anything that reacts to the presence of dangerous elements.
Of course, this can be taken in a literal approach of actually sending canaries into mines as well without discussing the concept of gasses killing them.
- In a Claude the Cat PSA, Claude warns against using gas in a caravan or you'll end up like a miner's canary.
- In the Ghost in the Shell: Stand Alone Complex episode "Pu239", a desperate worker falsified his records to state that his body had a high enough prosthetics count to work as a scrubber inside an abandoned nuclear facility. When he casually mentioned this on the job, a horrified coworker gave him a square piece of film and told him to get the hell out of there if it ever turned pitch black.
- Goblin Slayer: In the Water Town arc, the titular Goblin Slayer purchases a canary in preparation for Deadly Gas that the goblins may use, which turns out to be the case.
- Japan Sinks has Ayumu noticing some dead birds on the ground as she was making her way down into a valley. Moments later, her friend Nanami, who had gone ahead of her, drops dead on the spot: it is revealed that the earthquakes striking Japan was creating mazukus, pockets of extremely high carbon dioxide concentrations that are invariably fatal to humans and animals.
- Kenichi: The Mightiest Disciple has a variation on this with Kei Retsumin. He fights with a myna bird in a cage on top of his head. This is done because if he doesn't he runs the risk of using so much power he endangers himself. The purpose of the bird is to give out before he himself does, to warn him to dial it back.
- My Hero Academia uses a nonliving example when Todoroki and Yayorozu are fighting Eraserhead as part of an exam. Since they first don't know where he is, Yayorozu kept continually making small objects - when they stop coming out, that means he is near.
- Justice League of America (Rebirth): Lobo references this when Black Canary tells him that Batman has asked him to join the new league, saying "Ain't canaries supposed to go to the coal mines to die? That's what it said on your trading card, anyway."
- Nodwick makes a lot of jokes that one of the jobs of a henchman is to be the proverbial canary. Nodwick gets sent out in front of the party he works for on a regular basis so that he'll be the one triggering all the traps and attacked by all the monsters. He's resigned to it.
- A variation appears in The Far Side. A worker in a nuclear plant, seeing that the canary has sprouted a third eye, yells at his coworkers to run because the radiation levels have become dangerous.
- Played for Laughs in this◊ Mother Goose and Grimm strip.
- Referenced in one strip, where a worker who was a former coal miner gets reassigned so he's close to Wally. An observing Dilbert says, "Better get a canary." Scott Adams clarified this punchline in one of his anthologies, noting that "miners use canaries to sense gas..."
- Another comic◊ had the Pointy-Haired Boss get a (human-sized) canary to warn when meetings got too boring. It was already dead by the time he'd stated that canaries die of boredom before humans do.
Dilbert: I guess he knew that.
- When the hazmatted scientists in Arrival enter the alien craft, they bring along a bird in a cage just to see if "the air is clean".
- The titular parakeets of Bird Box are able to detect the ominous evil antagonists, beginning to chirp worriedly whenever they approach. The main character carries them around with her to act as this trope.
- In Close Encounters of the Third Kind, in order to test the government cover story of a deadly chemical spill at what is really an alien meeting site, the protagonists buy a canary as they enter the area.
- The Lone Ranger: Tonto scares the all the men out of the silver mine by walking around disguised as one of Chinese Laborers working the mine and carrying a cage containing his dead crow.
- Zygote: Canary Class synthetics like Barklay are used for mining operations in exactly this way, conditioned to regard themselves as more expendable than the higher class humans. However Barklay is told that she's actually human. Turns out synthetics are too expensive to waste, so the Mega-Corp buys a couple of synthetics to fool the OSHA inspectors, then makes up the numbers with cheaper human orphans purchased at a young age and raised to believe they are synthetics. Furthermore Quinn points out that using a synthetic for this trope would defeat the purpose, as an Artificial Human wouldn't die on hitting a pocket of methane gas, whereas the human Canaries would.
- In The Birds, the two lovebirds Cathy keeps in a cage get agitated at the same time the birds outside the house do, meaning that the characters can use them as a warning for when the attacks are about to happen.
- Feathered Friend, by Arthur C. Clarke. A pet canary on a Space Station keels over for no apparent reason. Someone remembers the history of this trope and checks the oxygen supply, discovering an air filter has frozen up, at the same time the alarms that would warn of this have been disconnected for a maintenance job.
- Little House on the Prairie: Pa and a neighbor are digging a well, and Pa always lowers a candle down and sees if it keeps burning before he starts the day's work. The neighbor thinks it's nonsense. As it turns out, Pa was right to take the precaution — one day, the neighbor doesn't do it and passes out from Deadly Gas deep in the ground, requiring Pa to rescue him.
Pa: All I know is, where a candle can't live, I can't.
- In Stephen King's The Stand, Center for Disease Control workers pump the air from the sealed hospital room of potential plague-carrier Stu Redman into the (likewise sealed) cage of a guinea pig named Geraldo, guinea pigs having been shown to be susceptible to The Plague. When Geraldo doesn't get sick after the usual communicability period (plus a bit more for safety's sake), they conclude that it's safe to enter Stu's room without an environmental suit.
- Used briefly in the Bonanza episode "The Emperor Norton", where the eponymous emperor accuses a mining engineer of not supplying canaries while working in the mine, after an accident. This leads to Joe going out and getting a canary for Emperor Norton to use as a demonstration.
- The George Lopez Show: In "Max's Big Adventure", George says that Carmen was "the canary in the coal mine" when it came to letting their kids walk to school on their own.
- In the Laverne & Shirley episode "One Flew Over Milwaukee", Duane the canary used to work in a mine. It didn't kill him, but it gave him bronchitis. Shirley adopts him and he's better by the end of the episode.
- Red Dwarf:
- In the series III episode "Body Swap", Rimmer — fed up of the consequences of Lister's non-stop curry diet — comments that he's thinking of getting a canary in a cage, to make sure it's safe for him to be in the room.
- In series VIII, Lister volunteers the main characters for the Canaries, which he mistakes for a singing group. It's explained to him via this trope that the Canaries are actually expendable convict soldiers who are sent to scout out derelict spacecraft. If none of them are killed, the important people are allowed to go on board.
- Sabrina the Teenage Witch: In "The Great Mistake", Hilda and Zelda recall some of the worst jobs they ever took over the years. Zelda had this happen to her when she was working in a mine:
Zelda: Chirpy? Canary's dead, let's get out of here. Oh push Aardvark, push!
- In the Chernobyl miniseries, the morning after the accident at the Chernobyl nuclear plant, a group of school children are walking to school when a bird suddenly drops to the ground and goes into death throes.
- The Colbert Report: In Beginning's First Dawn: A Tek Jansen Adventure: Chapter 3, the villain of the week takes over a planet and forces its inhabitants to mine a valuable mineral for him.
Into the mines! And don't mind that canary, he's just "sleeping."
- The Brittas Empire: Colin uses a canary in Curse of the Tiger Women to detect marsh gas present in the centre. Although it dies, its used to show that Brittas cooking really has been cursed by a gypsy (as it had a little bit of the food he prepared).
- The Police song "Canary in a Coalmine" compares the subject of the song to one of these (as if you couldn't tell from the title) due to his or her neurosis.
- Van Halen's infamous "No brown M&Ms" tour rider clause turned said candies into this trope. If the band members discovered brown M&Ms backstage, it was a sure sign that a promoter had not read the rider thoroughly and had almost certainly overlooked other requirements - ones that were actually critical to the band's safety.
- In Banjo-Tooie, Canary Mary is first discovered trapped in a cage inside a cave filled with Deadly Gas.
- Bravely Default references this trope in Eisenberg, where a mythril mine is located. Commander Goodman of the Shieldbearers brings up the subject to the player party, then reveals that the Swordbearers and Black Blades are using orphans as miners who they call "canary boys".
- In Day of the Tentacle, a canary is kept in a cage near a fireplace in a Colonial-era motel, to warn people about the smoke in case the chimney gets clogged.
- Deponia: In the alley, there is a parrot that when examined, you are told by Hannek that it is used to detect fumes in the mines. Upon which, Rufus asks what they do when that happens. Hannek's response is that they get a new parrot.
- In a video game based on Horrible Histories, you play as a canary trying to escape a miner.
- In Kittens Game, the description for Deep Mining is Yummy Canaries!.
- Viva Piñata: If you have a candary wear a gas mask, you can send it into a mine that you build.
- The Nitrome game Canary is inspired by this trope. You play as a lone canary in a mine colony, trying to survive an onslaught of alien parasites.
- Scribblenauts: In the "Underscore Mine" stage of Scribblenauts Unlimited, the first thing you encounter is a canary who wants some protection against toxic gas. Giving the bird a gas mask earns you a shard.
- SCP Foundation, SCP-2608 ("Anomalous Indicator Species"). SCP-2608 are an unusual type of mayfly that start dying off when they get close to an anomalous (super science, magical, etc.) item. They can be used to detect anomalous objects by moving them around and noting when they start to die.
- The web browser Google Chrome Canary is named after the practice, and quite aptly — it's the most experimental version of the browser, so it's very likely that whatever features they add could cause the browser to crash.
- In the "Joker Express" episode of The Batman, the Joker uses hypnotic lights in the rail-system to have other people steal for him. They then dump it in the river and he collects them. Batman, Robin and Batgirl track him down to an old mine. Here Joker is seen wearing a classic Railroad engineer outfit, complete with a small, handheld cage with a canary skeleton in it.
- An episode of Captain Planet and the Planeteers shows the origins of the Planeteers in flashback. Linka's shows a group of Russian miners escaping from a mine after the air goes bad. One of them, Linka's father, carries the now dead canary and laments that she will be devastated. She is.
- Spoofed on the Futurama episode "Fry Am the Eggman", when Bender lights up a cigar in a pub. A man on the next table has a canary, but it's the man who succumbs to the fumes, while the canary remains alive.
- In The Grim Adventures of Billy & Mandy episode "The Secret Decoder Ring", the secret of the universe can be found at the bottom of a mind shaft where the ghosts of canaries can be seen flying in and out, and couple of cockatoos and toucans and kiwis.
- An episode of Sabrina: The Animated Series had Sabrina and her friends go on a camping trip while being led by her Uncle Quigley. There, they hear a story from Harvey about a pair of canaries that were abandoned in an old mine when the miners evacuated the mine after it collapsed. When the canaries are found by Sabrina, Salem, and Harvey, it turns out that the canaries were alive and well, but actually dared each other into pretending to be suffocating, which scared the miners at the same time that the mine was about to collapse.
- The Simpsons:
- In the episode "Radio Bart", the citizens of Springfield are digging a tunnel to save a boy stuck on a well. At one point they find the canary dead and evacuate. Dr. Hibbert then determines that the canary died of natural causes and they go back to digging.
- One episode has Bart, Homer, Flanders and his kids out at sea on a raft. Homer thinks they're too far from shore, Flanders sees a gull and declares that they're saved, as gulls only come out to sea to die. The gull is then heard cawing and dropping dead in the water. Homer gloats that he was right and Flanders wasn't, and they're eventually rescued when they run into an offshore oil rig.
- Referenced in "Bart Stops To Smell The Roosevelts". After Jimbo makes a dumb comment, Superintendent Chalmers calls him "the canary in the coal mine of our failing education system."
Jimbo: You hear that? You're in my coal mine, bitches!
- Where on Earth Is Carmen Sandiego?: Subverted and discussed in-universe: Zack and Ivy found a dead-looking canary in a modern mine, and she told Zack they had to leave immediately. Zack told her not to worry, because (a) modern miners use electrical gas detectors, and (b) the canary was a mechanical bird, and in fact a clue planted by VILE.
- An online canary is the warrant canary, used to indicate a given website has received a secret subpoena enabled by the PATRIOT Act.