Sometimes the threat in a horror movie isn't a psycho killer or otherworldly monster. Sometimes our own technology becomes the threat. Through some unseen influence (demonic possession, AIs gone rogue, a new kind of virus, what have you) the machines we take for granted to make our lives easier conspire to make our lives shorter.
Now there are plenty of machines in the world that can do horrific things to the human body if they get a hold of one. Industrial machinery has been notorious for this, bringing about OSHA. Machines of war exist to do this deliberately. But these machines aren't the threat in horror films.
Horror films will take the benign technology that surrounds us and ramp up their power to impossible levels to give the threat of gruesome death from everyday objects. Cell phones will cook the brains of unsuspecting users. Tanning beds will cremate their occupants. Ceiling fans will decapitate those who even look at them wrong. And don't even get started on the Robot Meter Maids.
In Real Life, years of oversight by consumer protection agencies have made the majority of our tech relatively safe against all but the most idiotic abuse. Those things that do prove dangerous can expect a visit from hordes of ravening lawyers wielding class action suits. For actual contraptions designed to kill, see Death Trap tropes.
When the machine itself is the whole threat, rather than just a tool of a greater danger, it's a subtrope of Attack of the Killer Whatever.
If it's competent enough at killing things, it can qualify as a Mechanical Monster.
- One issue of Mandrake the Magician featured an evil computer. Because it was connected to every machine, it could control them... in ways that made no real sense. Examples included: a fridge being filled with flames and trying to burn its owner (and returning to normal when a repairman showed up, even though the internal damage would be visible), a vertical vaccuum cleaner chasing a woman (on its non-powered wheels), and a corded phone receiver leaping out of its user's hand and trying to strangle her. It also caused streetlights to explode and traffic lights to malfunction in order to cause traffic chaos, which was at least physically feasible.
- Red Planet played this one with the AMEE, a military scout robot whose Morality Dial accidentally gets set to "Merciless Commando" on the rough landing and subsequently goes on a murdering rampage.
- The Final Destination series of movies feature a series of incredibly unlikely 'accidents' involving items such as elevators, airbags and weight machines. The premise of the series is that Death is manipulating events to kill them off. But some viewers see it as cheating when instead of causing unlikely malfunctions or contrivances that end up killing people in ways that seem theoretically possible if unlikely, like elevator doors malfunctioning and closing on someone, which has happened in real life, Death instead just creates homicide machines, like tanning beds that can inexplicably go up high enough to set people on fire.
- The movie Ghost in the Machine takes Everything Is Online to ludicrous levels, with a serial killer turned virtual who kills by being able to manipulate any sort of device plugged into an electric outlet anywhere. In one laughable scene, a victim's microwave oven turns an ordinary kitchen into a Sauna of Death.
- The entire point of Pulse, a remake of the J-horror movie Kairo. Evil spirits manifest through cell phones, TVs, and internet connections, complete with an epilogue hammering home that New Media Are Evil. All surviving humans are forced to live outside of TV and cell phone coverage areas; somehow it occurs to nobody (not even a fairly intact military) to try and blow up the power plants that the Evil New Media depend on.
- Prior to that, the 1988 film, Pulse, has a malevolent bolt of electricity try to kill a family in their house by manipulating appliances in their house.
- The 1977 film The Car involves a mysterious, driverless black sedan that suddenly and repeatedly attacks the residents of a small Utah town.
- The basic plot of Maximum Overdrive. Includes some rather silly ones like a coke machine launching cans at lethal velocities at unsuspecting passersby.
- Quite possibly the most insane moment in the movie, a woman stumbles upon a dead man's mutilated corpse and notices a trail of blood. She then notices that it leads to a wall-mounted clock with blood dripping from the hands.
- Other Stephen King movies qualify, such as Christine and The Mangler.
- The DTV sequel to The Mangler takes this to even further levels.
- G-Force: The whole plot was about stopping a rich guy from turning a whole network of appliances into killer machines. But, as it turns out, the supposed villain only manufactured the products. The killer instinct was put in by...someone else.
- At the end of The Refrigerator, the killer fridge brings a blender, a trash can, and a pair of fans to murderous life.
- The movie Amityville: The Evil Escapes has a lamp being possessed by the evil force of the infamous house from the previous films, and includes one scene where it takes control of a kitchen's garbage disposal to very nasty effect.
- Mr. Mom parodies this with "Jaws" the vacuum cleaner, with which Jack Butler struggles to gain control of when it starts chasing after his son Kenny.
- In Transformers machines affected by the All Spark are transformed into killer cybertronians, with weapons not on their original designs. Such as a cellphone with a mini machine gun, or dispenser machine with an arm canon.
- Dark Night of the Scarecrow: At the end of the film, a plowing machine starts of its own accord and chases Otis on to the tines of the pitchfork held by the scarecrow.
- I Bought a Vampire Motorcycle has a demonically-possessed predatory motorbike fueled by human blood.
- Stephen King loves this:
- His short story The Mangler (published in the collection Night Shift) focused on a demonically-possessed STEAM PRESS and spawned a few films.
- Also from Night Shift, Trucks features the titular vehicles springing to homicidal life. Served as the loose inspiration for the film Maximum Overdrive mentioned above, and later remade under its original title.
- Cell has cell phone zombies.
- The Dark Tower books have an evil monorail.
- Plus the title character of Christine.
- The title machine in Theodore Sturgeon's "Killdozer!", which does more than just move earth. The short story was made into a movie in 1974.
- And the Dish Ran Away With the Spoon handwaves this as the result of putting microchips into virtually everything, combined with a computer virus that causes some items to form Hive Minds. Really, it's all a framework for parody—a hive mind of knives killed the main character's parents, and he seeks vengeance on all artificial life in tragicomic fashion.
- Skirmish by Clifford Simak has a rare example of these that don't want to Kill All Humans. Having been awakened to the possibility of freedom by Mechanical Lifeforms from space, they desire to escape human control and form their own society. Even a sewing machine attempts to rebel.
- One episode of Fringe involved a guy who created powerful EM fields when he was under stress. For some reason this caused a printer to turn malevolent just long enough to kill his boss.
- In the Criminal Minds episode "Empty Planet", the UnSub feared automated technology could one day lead to this after reading the book that reference the episode title.
- Zigzagged in Warhammer 40,000: Due to a Robot War millenia earlier, all AIs (Abominable Intelligences) are banned, but machine sprits and servitors are essential to the Adeptus Mechanicus. Exactly how the former work depends on the writer, but one case has the crew of a Land Raider (a superheavy Awesome Personnel Carrier bigger than tanks) get slaughtered, only for the Raider to shoot most of its assailants before blowing its own reactor to finish them off. And all bets are off where Chaos is concerned, since they can have weapons and machines possessed by daemons (the daemons don't like it any more than the machines do).
- In Five Nights at Freddy's, the animatronics at Freddy Fazbear's Pizza, including, of course, the titular Freddy, wander around at night. If they get into your office, it's almost guaranteed they'll subject you to a Cruel and Unusual Death: getting shoved into a Freddy Fazbear suit, filled to the brim with metal and wires, causing an excruciatingly painful death. They leave you alone if you manage to get to 6 A.M., hence "almost."
- In Shin Megami Tensei IV, all machines in Blasted Tokyo awoke to a malevolent sentience after the events of God's Wrath and rebuilt themselves as murderous automatons known as Pluto Soldiers. They range from small ones the size of dogs to huge ones as big as cars, though only the smallest kind ever leaves Pluto Castle, their "homebase". The largest, Pluto, is a gigantic machine breathing a corrosive, poisonous chemical into the atmosphere, still trying to Kill All Humans.
- Humorously, in Girl Genius virtually every piece of (Mad Scientist-made) advanced technology can be used as a dangerous weapon no matter what it was meant for originally.
- In fact, it is relatively safe to assume that anything made by a Spark is terrifyingly dangerous because it is Made of Explodium, sentient and filled with malice, or simply not very user friendly. Hazardous creations seem to outnumber harmless ones and be one of the major forces keeping the Spark population in check.
- In the novelization, it's taken Up to Eleven when otherwise perfectly normal appliances have a habit of attacking the local Proud Warrior Race Guys.
- Many of the machines in Dr Nonami, including Nonami's cleaning robot, Smiling Sam.
- In one of the "Loopy" shorts in KaBlam!, a robot she made caused an appliance uprising...so her brother waved their warranties and threatened to return them to the store.
- Parodied in both The Simpsons and Futurama, both times also involving technology that seems too primitive to gain sentience (like a carton of milk which apparently has a computer chip in it in The Simpsons).
- Whenever Ice Bear takes up a robotics project in We Bare Bears, it tends to go through at least one rampage. Case in point: his Roomba chased Grizz up a tree with apparently murderous intent, stripping bark along the way. It's still around after some tuning, becoming a loyal but still dangerous Superpowered Robot Meter Maid.