Living Motion Detector

A Living Motion Detector is a person, monster, or robot that can only detect you if you're moving. Depending on its level of intelligence, it may forget about you when you stand still, or it may go looking for you. A common tactic in combating one is to somehow make objects around you move while you yourself stay still, causing it to attack the moving object instead of you.

Usually such things are antagonists who would otherwise be overwhelmingly powerful.

Examples of Living Motion Detector include:

Anime and Manga

• Notorious B.I.G., a Stand in JoJo's Bizarre Adventure: Golden Wind, has this trait. Trisha managed to confuse it by using her Stand to shake the chairs on the train she was riding, leading it to attack them instead.
  • Dio's raptor form in Steel Ball Run
• In explaining why their zombies are different, Highschool of the Dead posits that, since the brain and the optical nerves are dead, zombies detect through vibrations instead of visual signifiers. This can be useful for distracting zombies, as a wet cloth thrown against a locker will cause a horde to turn away from the human standing right in front of them.

Film

• A variant in Pitch Black, in that the monster can't see you if you stand between its eyes, because of a dead angle caused by their armored heads.
• The underground Graboids in Tremors can only detect you by the vibrations caused by your movements.
• In a variant, the Blind Dead from the Spanish film series of the same name can only track you down if you make a sound. Staying still helps. It can't save you forever, however -- they can hear your heart beating.
• The Deadly Spawn has very toothy grinning aliens who are blind but hunt by sound. Be very quiet and it won't notice you.
• According to the featurette from "How to Train Your Dragon", if a viking stays in a Deadly Nadder's blind spot directly above its nose, they are relatively safe - http://www.youtube.com/watch?v=dygaH9nb6WU

Literature

• The Tyrannosaurs in Jurassic Park. This is a side effect of its frog DNA (frogs really can't see prey if it doesn't move).
  • Not true. In the first Jurassic Park novel, several of the characters thought that the T-Rex could only see motion like a frog, but the frog DNA was never part of this explanation (just an Ass Pull explanation for why some of the dinosaurs could reproduce). In the second novel, it was explained that T-Rexes could see things that were standing still perfectly well, as one man fatally found out. The T-Rex in the first book had just been ignoring the humans because it wasn't hungry.
• Hunter-seeker robots in Dune.
• In Piers Anthony's On a Pale Horse (Incarnations of Immortality #1), Zane faces off against a demon that looks like a 5 meter tall preying mantis. He realizes that it can only perceive him as prey if he moves. (And he can even do that as long as he doesn't move in a way that resembles the motion of prey.)
• The dragons in the Steerswoman books, which are actually robots.
• An interesting variant in Terry Goodkind's Sword of Truth series, a screeling can see you if you run or if you stand still, but not if you walk slowly.

Live Action TV

• Angel:
  • The assassin in "Blind Date" is blind but has learned to detect "other parts of the electromagnetic spectrum." The net result is that she's a human example of this trope, at least when she's fighting someone like Angel who doesn't generate body heat.
  • Also:

The Groosalugg: I once happened upon a herd of Bur-beasts and as you know, engorged Bur-beasts will couple with Anything That Moves. I was forced to stand perfectly still for eleven days and nights.

• The Raston warrior robot from the Doctor Who episode "The Five Doctors."
• The monster Silvagon of Ultraman Tiga could only see movement, leading to a hilarious scene where Ultraman strikes at it, then freezes up as soon as it turns to face him. This gets especially silly when he's forced to hold a precarious crane stance. Eventually Silvagon gets fed up and starts blindly running around, lashing at the air.

Video Games

• One of the boss creatures in the original Half Life was a massive but completely blind tentacle that detected you by your footsteps. You could either crawl past silently, or set off an explosion and run past while it struck at the louder noise.
• Similarly, Los Garradors in Resident Evil 4 are blind and hear your movement if you're running, as well as your commands to Ashley. Sadly for them, you fight them in the vicinity of bells - one strategy for defeating them involves shooting the bell and then shooting its weak point (For Massive Damage) while it's distracted. Another is simply walking, which they can't hear.
• One of the enemies in Yoshi's Island is a ghost with big wraparound sunglasses to denote blindness; it homes in on Yoshi whenever the cute little dinosaur makes a sound. That includes jumping, throwing eggs, or even touching coins; the ghosts have good enough hearing to hear the obligatory video game blips and beeps. To add to the fun, the ghost can only home in on the place where you last made the sound, and looks quite clueless and confused when you aren't there.
• The Berserker from the first Gears of War was blind, but could detect where you were through your footsteps, as well as your smell.
• The Witch from Left 4 Dead doesn't seem to care about you until a) get really close, b) make a ton of noise in her direction or c) blind her with your flashlight. Then she gets pissed, and it's Losing Your Head time!

Web Comics

• The clank in this Girl Genius comic.

Western Animation

• Poked fun at in Family Guy where Peter and Lois encounter a prostitute who sees by movement.
• Phineas and Ferb and Candace travel back in time and encounter a T-Rex, Phineas advises this technique and admits his surprise that it actually works.
• Toph Bei Fong is blind, but can feel and hear so well (especially through dense, solid materials) that the vibrations generated by footsteps allow her to fight easily. Late in the series, she can even detect people by their heartbeat and tell whether or not they're lying.

Real Life

• This is Truth in Television for some animals.
  • Frogs are extremely near-sighted, but capable of detecting movement at a distance.
  • Many insects. The compound eyes present in many species are awful at making out detail, but excellent at detecting even minute movement.
  • As well as many fish.
• Dogs are visually more attuned to motion than color.