It's a wonderful device a detector that detects the things you need! There is a detector for everything — Applied Phlebotinum, Green Rocks, guns, bombs, spaceships, ghosts, mice, cheese, socks... If you live in a high-tech setting and need to find something, there is a type of The Little Detecto that will detect it!
The physics behind the Little Detecto is never explained. It just detects the thing that is the local Serious Business.
The trope namer is a gadget from one Tom and Jerry cartoon that was used to detect mice.
- About the only good thing about the Brand of Sacrifice from Berserk is that it lets Guts know when the demons are coming for him by bleeding.
- In Digimon Tamers, the D-Arc is able to detect where are the Digital Fields, which contain Digimon that crossed to the real world.
- Every version of the Digivice has something like this, detecting either Digimon, Upgrade Artifacts, rifts that can let someone travel between it and the human world, and so forth... pretty much whatever is needed.
- The dragon radar in Dragon Ball, made by Bulma to find the Dragon Balls. Handwaved by saying that the Dragonballs emit a special kind of radiation in the first chapter of the series.
- In Love Hina, Kaolla Su produces a device that detects turtles... and some kind of pot, the two words being homonyms in Japanese. She later upgrades it to detect Keitarou and Naru.
- On Pokémon, Officer Jenny (Junsa in the original) just happened to have a sleep wave detector in her pocket when the situation called for it. Dogasu (he compares the dub to the original) says here:
The whole thing is fine at first. We're presented with a mystery, and for a little while there the story makes some very logical progressions...but then everything just goes all to hell when Junsa (and, later, the Rocket-Dan) pulls out a freakin' sleep wave detector. Because, y'know, that's what police officers just happen to carry around with them at all times. I can totally imagine Junsa's orientation day at the police station. "OK...here's your badge, your gun, and your standard issue sleep wave detector. Good luck."
- In addition to being the source of a Magical Girl's power and their effective phylactery, Soul Gems in Puella Magi Madoka Magica are also handy Witch detectors as shown in the second episode, glowing brightly when they're close to a Witch's presence.
- In YuYu Hakusho, when Yusuke and his teammates need to locate Hiei, Botan mentions the Spirit Detective Tools. The Demon Compass finds demons by measuring demon energy. The Mystic Whistle is a whistle for demons that functions like a dog whistle; it causes Hiei to appear.
Hiei: I only came to find the source of the vile noise... and kill it.
- The HEYDAR and the BTRS Meter on The Middleman.
- In the Warhammer fic An ISOT In Grimdark, German scientists invent special "magic indicators" that prove invaluable in helping detect concealed magic wielders and dangerous magical artifacts like the warpstone bombs...
- In the Harry Potter fic Mr. Black and the Demoness, a mad scientist friend of Harry's made a "Dork Lord" detector out of an old alarm clock.
- The Return, pattern detectors. Little palmtop things that tell you if the creature currently ripping your heart out through your ribcage is a demon or not.
- The motion detectors in Aliens use changes in air pressure to detect movement.
- From the first movie:
Ripley: What's it key off?
Ash: Micro changes in air density.
- Very small changes in air density are what we call sound. So, it's a microphone?
- From the first movie:
- Of course, the PKE (psycho-kinetic energy) Meters (for detecting ghosts and ghost phenomena), Ecto-Goggles (for seeing invisible ghosts), Giga-Meter (maybe for environmental psychokinetic effects?), and the ghost-sniffer (may be a real-world gas detector for crossing off "hallucination stemming from gas inhalation," may be an in-universe paranormal detector using a real-world detector as a prop), all from Ghostbusters (1984).
- X-Men: Days of Future Past features special devices capable of detecting the Mutant X-gene ... as early as 1973. Makes you wonder why the government didn't use those in any of the films set later...
- Chrestomanci: In Witch Week, Inquisitors carry witchcraft detectors. Chrestomanci's, however, is just a cigarette case that he causes to beep at appropriate times; he doesn't need a machine to tell him when someone's a witch.
- "Numbers" Riktor, from the Discworld books, designed numerous Little Detectos for different things. The only one that became relevant to the books was the resograph, which alerted the wizards to a serious incursion in reality.
- Probably named after the Richter Scale.
- The thaumometer, as used by Ponder Stibbons and others, is the Discworld examplar of the universal Everything Detector.
- The swords of the Nac Mac Feegle glow when they're near lawyers.
- Frodo's sword Sting from The Lord of the Rings glows bright blue when the orcs draw near.
- As do Glamdring and Orcrist, the swords Gandalf and Thorin acquired at the same time Bilbo picked up Sting in The Hobbit.
- In Mistborn, bronze Allomancers (also known as Seekers), can detect Allomancy. The most basic level is simply being able to sense when Allomancy is being used and who's using it, but more skilled Seekers can detect what metal is being burned, whether or not it's being flared, which emotions a Soother or Rioter is trying to affect, and even how much metal the Allomancer has left.
- Blake's 7: The Terran Federation created a "Molecular Shift Detector", which could detect the sudden air-displacement caused by using a teleporter. The resemblance to the working principles behind the motion-detectors from the Alien franchise, the first installment of which was released during the show's run, is probably not wholly coincidental.
- Doctor Who:
- The Doctor's sonic screwdriver is often used in this fashion.
- In "The Time Monster", the Doctor tracked down the Master with a device that Jo christened "a TARDIS sniffer-outer".
- "The Android Invasion", in which androids are passing as humans, has a robot detector. It's a small box with a single red indicator light on it.
- "Blink" memorably featured the timey-wimey detector. It goes 'ding' when there's stuff.
- "The Day of the Doctor": The Tenth Doctor has a gadget intended to detect Zygons. However, it's not quite as reliable as he'd like.
- In The Flash (2014), Earth-2 has a cellphone app that can detect nearby Metahumans.
- Molly Walker from Heroes can find people.
- The Muppet Show: Bunsen Honeydew once invented a gorilla detector. It completely failed to detect the gorilla until after it had already attacked his computers, and him. Bunsen originally attributed the failure to the fact that the attacker was not actually a gorilla.
- In People of Earth a guy at a UFO convention has a device that he claims detects cosmic radiation on people, but Alex is quite skeptical when he claims she has a very high level of cosmic rays, indicating she's been to space.note She thinks the wand looks like a curling iron. But, later Don passes by the booth and the device goes crazy.
- Stargate Atlantis features the Life Signs Detector, about the size of a PDA and highly useful in many situations.
- Star Trek has the ubiquitous tricorder, which is half this trope and half hand-held Everything Sensor.
- BIONICLE has the Kanohi Elda, Mask of Detection. It functions as a detector for the fabled Mask of Life, and signals to its wearer with an ever-intensifying headache. And it can't be turned off. Yeah, nasty mask... but when the situation called for the Mask of Life to be located, headaches were among the least of the wearer's worries.
- Our Miss Brooks: Walter and Miss Brooks use a Geiger counter in "Rare Black Orchid" to search for uranium. Walter had discovered some on his shoe and concluded he had unknowingly stepped in uranium recently.
- In Dungeons & Dragons, many spells work like The Little Detecto. They have titles beginning with "Detect", as simple as that. Detect Magic, Detect Evil, Detect Undead, Detect Traps...
- There's also "Locate City", but that's mostly known for a trick called the Locate City Nuke. It involves placing 4 different metamagics on the otherwise harmless spell so that it becomes a viable target for putting a metamagic spell that throws people outside the range of the spell. Since Locate City's range is measured in miles and being thrown out of the range does 1d6 per ten feet, it kills pretty much everything in range, including the caster.
- Lesser Globe Of Invulnerability, a normally useless spell, comes into play here as it can stop you being thrown the 400ish miles for over 200,000d6 damage.
- The Detect advantage in GURPS, of course. In the Magic book nearly all the spells relating to this stem from "Detect Foes".
- The most basic building block of Enhanced Senses powers in the Hero System. For example, radar is basically "Detect objects that reflect radar signals" with some modifiers tacked on to make it work like proper radar in terms of game mechanics.
- In Mistborn Adventure Game, bronze Allomancers (also known as Seekers), can detect Allomancy. The most basic level is simply being able to sense when Allomancy is being used and who's using it, but more skilled Seekers can detect what metal is being burned, whether or not it's being flared, which emotions a Soother or Rioter is trying to affect, and even how much metal the Allomancer has left.
- Auspexes in Warhammer 40,000 range from handheld devices to helmet-mounted trackers, mostly used to track invisible enemies, though some can be used to detect incoming enemies. Unfortunately, they can apparently only be calibrated for one species at a time, and if there's something not entirely human about...
- Orks use a lifeform detector called a Gitfinda'. It finds gits so they can get to the fighting without wasting time looking for targets.
- Beyond Good & Evil has both the Pearl Detector and the Animal Detector, which help you find Plot Coupons and animals for your First Person Snapshooter sidequest.
- In Dishonored, The Heart lets you detect runes and bone talismans, and can tell you secrets about people you point it at.
- The Elder Scrolls III: Morrowind had three detection spells, Detect Magic, Detect Creatures, and Detect Key. While the last was very handy, one wonders what aspect of keys makes them detectable vice any other particular object. (Although it does serve a kind of Mundane Utility verisimilitude. One can only imagine a wizard inventing it after turning his laboratory inside-out trying to figure out where he left his keys last night.)
- In Final Fantasy IX, the chocobo acts as this while you ride it. They are able to detect things buried in the ground, and a text bubble appears for you to play Hot and Cold as you run around to find the item.
- Cole from inFAMOUS has the inherent ability to detect nearby Blast Shards, the general direction of dead drops and sources of electricity, including ones in people. This is denoted by icons on the radar and a quick Aura Vision onscreen.
- In Metal Gear Solid 2: Sons of Liberty, a bomb disposal expert creates one which specifically searches for the aftershave his Apprentice turned Mad Bomber applies to all his bombs. It turns out he no longer applies it to all his bombs.
- In the Pokémon games, there's also the Item Finder, which shows you when you're close to items... which can be everything from medicine, to Poke Balls, to glass flutes, to chunks of gold. How it picks these up and ignores everything else is never explained other than "It's just a game, relax."
- In Diamond and Pearl, in the Sinnoh Underground, you also have a "radar" which lets you find things buried in the ground and walls. These can be both traps and "orbs," which you use to buy things down there.
- Pokémon Colosseum has a character that can detect an "aura" around Shadow Pokemon. XD replaces her with a device that looks like a DBZ Scouter.
- The Powder Toy has DTEC. It generates electricity when a specific type (defined by DTEC's ctype) of particle touches it.
- Rainbow Six Siege has IQ's electronics detector and Pulse's heartbeat sensor.
- Sam Fisher's goggles in Splinter Cell Chaos Theory gain the ability to view electromagnetic fields, which essentially shows the player electric/electronic devices they can interact with.
- The S.T.A.L.K.E.R. series has the Artifact Detectors, though they only really appeared in Call of Pripyat after being Dummied Out of the earlier installments. There are several different versions, the best of which leans slightly towards being an Everything Sensor as it can also mark the position of non-moving anomalies.
- Starbound has the Ore Detector, which sends a pulse that detects different ores in the screen you're in, even if they're within the ground.
- Viscera Cleanup Detail provides a detector as one of your core tools. Toggle it one way and it detects any liquid waste, the other and it detects solid waste. It's incredibly sensitive, able to find things that are nearly (or entirely due to physics engine weirdness) invisible, and can even detect dangerous living organisms or anchors for most incorporeal malignant entities. While it's theoretically possible to get almost any area perfectly clean without using your detector (provided you're painstakingly careful never to make the slightest extra mess yourself), detector sweeps aren't really optional.
- In the Warhammer 40,000 game Dawn of War II—Retribution, during the Ork Campaign when pursuing teleporting Eldars, trusty second in command Mister Nail-Brainz set his git-finda to "Pansy" mode.
- Antares Fairchild's route of Starship Promise kicks off because the protagonist has invented one of these which picks up signs of alien life from outside the known galaxy. Upgrading the device (which the protagonist has named the Blip Bop) occupies most of Antares's first season.
- In The Fairly Oddparents, Mr. Crocker has a "fairy detector" that he uses to hunt down Timmy's fairies.
- In Futurama, Bender once claimed to have built-in Gaydar.
- Leela has "This thing on my wrist" which sometimes acts as one.
- The robot convention had a Soul Detector. If anything sentient came walking in, they had to pay an admission fee.
- Bender once went looking for frozen mammoths.
Fry: The ship has a mammoth detector?
Bender: You're drunk, Fry. This is the elephant detector. I just set it to big and woolly.
- Phineas and Ferb:
- In "Vanessessary Roughness", Dr. Doofenshmirtz "just happens" to have a pizzazium detector in his top pocket after he and his daughter stumble upon a sample at the mall. It comes in handy when Baljeet snags the pizzazium first.
- In "The Chronicles of Meap", Phineas converts a GPS into a "cute tracker" to find an adorable alien the boys call "Meap". Isabella, who harbors a crush on Phineas, is annoyed that the device apparently ignores her, until Phineas reveals that he deliberately had it ignore Isabella's cuteness. When he adjusts the device to stop ignoring Isabella, it self-destructs.
- Spoofed on The Ren & Stimpy Show episode "Marooned". Cadet Stimpy pointed one such device at various things on a strange planet, but all that he found out was that "this thing makes the coolest noises."
- Gargamel had various items used for detecting Smurfs in The Smurfs cartoon show.
- At the end of Xiaolin Showdown's first season, Jack Spicer builds a Shen Gong Wu detecto-bot.
- Metal detectors work by sensing changes in permittivity. Chunks of metal cause this. So do other, non-metal objects, like say a large chunk of meat (in the opposite direction, so it's possible to discriminate between the two, though the cheapest, most primitive kinds don't).
- Bomb detectors are usually "sniffers" that detect volatile materials given off by the explosives. Or they're glorified metal detectors. Or they're X-ray machines that display something that causes an attendant to think "Hmm, that looks bomb-ish."
- "Gun detectors" ditto. Basically just metal detectors or X-ray machines that display a suspicious outline.
- Geiger counters detect ionizing radiation. They're wonderfully agnostic about the source, so they'll happily go nuts if you point them at, say, a cathode ray tube. They're also remarkably insensitive to gamma rays unless properly constructed; they actually react to secondary electrons kicked out of the material surrounding the detector tube by high-energy photons (gamma rays).
- The Church of Happyology uses these. Depending on who you ask, they detect how unhappy you are, or how many dead souls have glomped onto your body. Or maybe how tightly you grab the metal cans of the thing.