Robots aren't scary enough. We need to rectify this.

The basic principle of zombies as a monster of horror is that they represent the inescapability of human mortality. Zombies are slow, dreary, lurching, almost pathetic creatures which nevertheless inevitably overcome all obstacles and, one day, while you're asleep, will get you and remove your capability for life and turn you into one of them. In 28 Days Later they move at some furious speed which kind of defeats that metaphor, even if it does make them substantially scarier. That's the premise, though.

Vampires seem to have all kinds of clever superpowers and a hodgepodge of bizarre weaknesses. The precise items making up those two lists varies from canon to canon, but in most cases it's a bit of a mess. I've never really "got" vampires as a subject of any substantial interest, I don't see how they're supposed to be scary or threatening or interesting or noble. This opinion probably results from never having experienced much in the way of vampire fiction, but also, vice versa, so, whatever. Anyway (and this is an evaluation I've pretty much stolen from elsewhere, but I think it's logical), vampires represent fear of sex and intimacy.

Werewolves symbolise the dangerous, primal, animal nature of man which is just waiting to surface given the right trigger.

Aliens represent foreign people. Alien cultures hold the mirror up to humanity and show us ourselves.


As monsters, I hold that robots represent the threat of technology. Robots warn us that the human race supplanted more primitive ancestor species and that, one day, we, too, may be supplanted by our offspring. Robots are the fear of science advancing so far and so fast that we are left behind and then killed for not keeping up. Robots are smarter, faster and stronger than we can ever be.

Except for the "faster" bit. See: Cybermen, Terminators. (Aside: following Aliens and Predators, any bets on there being a movie entitled Terminators soon?) My basic observation is this: robots are metal, mechanical devices. As a result of our perception of mechanical devices in reality, robots are typically depicted as being slow and plodding, even if they are tremendously strong and typically bullet-proof. But robots, by their very nature, should be able to react infinitely faster and with infinitely greater precision of action than an ordinary human. It is consistent, both with logic and the metaphor, for robots to always move faster than the human eye can even follow.

It is not logically consistent for humans to be able to fight robots and win.


When a robot shoots at you, it does not miss. When you peek out of cover to see if the robot knows where you are, the robot shoots you instantly. When you run between cover to try to draw the robot's fire, the robot shoots you instantly. A robot does not have reaction times. A robot does not hesitate, it kills you.

A robot doesn't need to shoot you anyway. By sacrificing its heavy steel frame, armour and armaments for lightweight aerospace materials, my robot, while more vulnerable to physical damage, can move - on foot - faster than the human eye can see. That means it can get to you and punch a hole in your carotid artery - and the carotid arteries of all your closest friends - in the time that it takes you to realise that there is a robot cresting that hill over there. Maybe it uses a knife. Maybe it just kicks you in the throat with one sharpened toe at a hundred and fifty miles per hour.

A robot doesn't pause. A robot doesn't wait. A robot doesn't catch its breath. A robot doesn't stop to think, plan, plot or scheme. If it created a plan, you didn't notice, because the plan was created in a matter of milliseconds, while the robot was in motion towards your carotid artery.

You'll never see it, because it moves so fast - and keeping the monster hidden is one of the greatest principles of horror - but if you slow down the CCTV footage of my robot escaping the facility where it was constructed, you'll see that it looks emaciated, flimsy and whiplike, like a skeleton made of lightweight fibreglass reeds and car radio antennae, like the spider zombies from Ravenholm but with a belly full of battery and enormous freaky exposed binocular camera eyes. It moves at the speed of Rat Thing from Snow Crash. It doesn't move like a human or even like a regular creature but flails at the ground like some rabid monkey, some wild alien insect. Its electric battery - which can propel it at top speed through five carotid arteries per second for maybe a month and a half - buzzes angrily and loudly and is the only sign that the thing is approaching. "Approaching", not "nearby". The robot does not stand still for long enough to be "nearby". It's either coming towards you at high speed in order to kill you, or you're dead.

If we're still going with my personal vision, then I will add that the robot can't hear - the noisy buzzing battery would make that impossible. It can't speak, because it's not intelligent. And it can't learn or solve problems beyond basic pathfinding, because it's not intelligent.

Why is it not intelligent?

  1. It doesn't need to be. Its sheer speed makes up for all of this.
  2. From a storytelling perspective, intelligence accords the machine a slight capacity for reason, emotion, thought and even sympathy. Robots without these things are more efficient killers.
  3. Adding AI to the machine would, for me, subtract greatly from the plausibility of the premise. A machine that can think has always been well over fifty years in the future. In my opinion - and I might be drawn upon to explain my reasoning another time - human-level AI is actually impossible, at least for humans to create. On the other hand, a simple BigDog which (1) moves at 150mph and (2) kills people is at least ninety-nine percent possible, right now.

So it can't learn. Lucky you.


So how do the humans win? After all, the humans have to win.

A substantial number of independent - or, heaven forbid, cooperating - robots would shred a whole continent in a matter of weeks, but given a sufficient lead time, here is how you kill one:

Construct a very large static magnetic field and bait it so that the robot runs through the field at high speed. The movement of an electrical wire through a magnetic field induces a current in the wire. This fries the robot's CPU.

An electromagnetic pulse could also work, but would be infinitely more difficult to set up. A simple electromagnet can easily be constructed anywhere that there is cable and power.


Are you ready for the robot revolution?


Discussion (54)

2010-05-11 22:44:53 by Josh:

I really like this analysis. It always bugged me the way the Terminator movies had robots building robots to fight humans that were far less compliant than the humans they were fighting. Then in the Matrix sequels you had the sentinels that spent more time buzzing around in circles than actually killing anything. The only film where this is even remotely justified is I, Robot where they were designed to look and act human and their programing wasn't to kill everyone (not primarily, at least). I just wish someone would actually use their heads and make a believable killer robot for the 21st century.

2010-05-11 23:09:15 by Solteur:

My vision isn't quite that scary, mainly because I don't see a robot moving literally too fast for the human eye too see. After all, it's got all that annoying mass and whatnot. But it's true that the "robot from the future that moves slightly faster that granny with a walking frame" is rather ridiculous.

2010-05-11 23:11:43 by Solteur:

@ Josh True, I, Robot did the "fast, scary robot" thing quite well.

2010-05-11 23:19:49 by Tom:

Why does the robot need to be human shaped? Other than it representing a more advanced version of ourselves, there is no need for it to be... It could be scarier if it had crazy numbers of limbs or whatever.

2010-05-11 23:22:07 by qntm:

"Because it's a more advanced version of ourselves" is exactly why it must be recognisably human. Or highly deformed, grotesque human.

2010-05-11 23:38:00 by BenFriesen:

I'm a little surprised to hear you say that you don't think human-level AI is possible for humans to create. I've read everything on this site from Fine Structure on down, and I had supposed that we were of a like mind on that issue. I'd really be interested in hearing why you think that's the case. What about humans making progressively more accurate simulations of the human brain? One of the things that I like about this concept of robots is that it would allow a film to have great bullet-time (which, as a college-age male, I am a fan of). If you wrote a story, it would have some of the great hyper-time passages that your Powers stories have. I suppose the difficulties in actually making this into a workable plot is that so many people would die; horror usually relies on close-calls.

2010-05-11 23:59:42 by qntm:

I'll answer this in more detail tomorrow morning but for starters Fine Structure is a work of fiction.

2010-05-12 00:14:24 by Dirdle:

Isn't there a problem, for film at least, with an enemy that's too fast to see most or all of the time that it's "on camera"? I suppose you could go overboard with slow-mo, but (I'd say) that's only barely an improvement. On the same direction of though, I'd think the "advantage" of an EMP over the 'lure into magnetic field' idea is that is both an active device (a weapon, not a trap, which seems more appealing in (soft) fiction (to me)) and that it is more reasonable (still wrong, but whatever) to use flashy effects with one. Boom! Explosions! Lightning! Robots ceasing to function! I agree with the idea. In a written medium, this is definitely scarier and more plausible than the "walking brick" approach. In film, it might be - it depends how appealing the "bullet time" can be made, especially when said scenes will consist of a robot slaughtering completely static humans. As BenFriesen points out, stories - even horror stories, unless you're H.P. Lovecraft - need to have protagonists who can do more than "stand still in bullet time while the robot pokes holes in you."

2010-05-12 00:28:20 by Josh:

Another thing that always bugged me about killer robots is how the humans always treated them like independent entities while fighting them as opposed to a "hive mind," which is exactly how they'd function. Did that robot see you at all before you killed it? If so, every robot in the area (or on the planet, depending how good their signal is) knows exactly where you are and what you look like. That trap you sprang on it will not work the same way twice because now every other robot out there has been reprogrammed to detect and avoid it. This all assumes, of course, that the machines are as smart as most fiction stipulates.

2010-05-12 00:30:26 by Jake:

They did something like this in Screamers ( ) The main robots were small, fast buzzsaws that would burrow underground, only popping up at the last second to turn your face (and the rest of you) into hamburger chunks. They emit this high-pitched screech as they came at you, from the mechanics whirring as they speed toward you. They also had infiltrator units (a la Terminator) that looked human. That is, until they get you alone. Then the metal blades burst from under their skin and slice you to pieces. So at least somebody else has had this same idea.

2010-05-12 03:50:27 by sunburstbasser:

A killer robot should have a very wide visual range. If it is only capable of human level sight, it will be less effective in low-light conditions. It would need infrared scanning as well.

2010-05-12 06:29:38 by Daniel:

I don't see why it should be so fast. Especially if you expect it to ram into people. That would destroy it. Even if it doesn't run into people, at that speed it will run out of fuel very quickly. Why not just blind it with a flashbang? It will probably kill the guy that throws it using the trajectory of the flashbang, but now it's useless.

2010-05-12 08:50:45 by Azrael:

>On the same direction of though, I'd think the "advantage" of an EMP over the 'lure into magnetic field' idea is that it is more reasonable (still wrong, but whatever) to use flashy effects with one. Boom! Explosions! Lightning! Robots ceasing to function! Well if you posit an EMP weapon powered by a Flux compression generator (, which some of the ones currently being researched are, then you can at least plausibly have an explosion.

2010-05-12 09:15:07 by Crane:

Next week on [GENERIC MEDICAL SOAP OPERA #37] "Oh God, the SCARY ROBOTS are coming closer, whatever shall we do, Doctor Von Hansomm?" "Never fear, nurse!" *twirls moustache* "We shall thwart their mechanical machinations with the power of this MRI scanner!" On a more serious note, I really do like this idea as a horror movie... As you said, how often does anyone try and make viewers scared of robots?

2010-05-12 09:47:53 by Michael:

"vampires represent fear of sex and intimacy." No. No no no no no no. That's the stupid new Twilight vampire. True vampire stories delve into how becoming a vampire is a deal with the devil: immortality for the price of being an ugly, unattractive *thing* that can only go out at night.

2010-05-12 11:43:17 by jonas:

Where did you get the idea that robots were slow in fiction? In the Asimov books, the robots – except for the first ones – are very fast and have a fast reaction time too. (They're also intelligent and so they sometimes try to conceal their speed when they want to pass as a human.)

2010-05-12 12:35:04 by qntm:

They're also not scary. Asimov's robots have a different narrative purpose from scary robots.

2010-05-12 14:15:00 by Thrack:

How about the killer robots from the book Daemon? (Its a sci-fi thriller.) They're shaped and move like motorcycles and can temporarily blind people with laser light just before decapitating them with two blades they carry on either side. I think they might have a way of going up stairs too but I forget what it is. Oh, and they travel in packs.

2010-05-12 16:42:02 by DrT:

AMEE, the malfunctioning robot in Red Planet, is freaking fast. But since it is lightweight the humans have a chance of fending it off nonetheless. And that is probably the answer to your problem: If you have robots that are strong, fast, robust, and intelligent, then you have no story. At least not one withing the typical monster genre.

2010-05-12 16:50:43 by Knut:

I second the request for a more detailed explanation of why you think humans will never create strong AI, also, great concept! Doing for robots what "28 Days Later" did for zombies. Though it would still be possible to barricade yourself from them, since humongous speed is at odds with concrete-shattering strength.

2010-05-12 20:14:59 by sunburstbasser:

The robot from the movie Short Circuit was originally supposed to be a scary robot. Using treads instead of limbs allows it to move very quickly and traverse different terrain. In the movie the robot uses a piece of a car to deflect bullets fired from a high-powered rifle, so it is capable of quickly determining trajectories and defending itself from bullets. And it has pin-point precision with a shoulder mounted laser. In the beginning of the movie one of the robots smashes solid ice with it's fingers, so it is certainly strong. With the proper writing, such a robot could have been frightening and maybe is a solid prototype for Sam's killer robot.

2010-05-12 22:02:23 by Anon:

Third for AI explanation. Though I still think we'll kill ourselves before we make a human-level AI. Since the robot would be lightweight, wouldn't that mean that it wouldn't be able to pierce thick walls? Car antenna wires traveling at 150 km/h would cut through most things, but brick walls should stand a chance. But they're probably coming in through the windows.

2010-05-12 23:11:41 by FinDude:

If a machine wants to kill humans, it's broken. When something's broken, you fix it.

2010-05-13 00:45:46 by Thrack:

FinDude, that would mean a tank is broken. Or a grenade. Or anything else a soldier might have that's designed to kill people. Sure, they don't *want* to kill people but wouldn't that require higher level functions generally attributed to strong AI, which isn't what we're talking about here, like in The Terminator? Hmnn... how about using utility fog as a killer robot swarm?

2010-05-13 08:15:59 by Memento:

The problem with saying that a tank or gun or w/e is broken if it wants to kill people is that they are tools, not robots. Conversely, a robot that wants to kill people is one that has been programmed to kill people. This is something a human would have had to do at some point or another - and we all know how much inhumanity man is capable of to his fellow man.

2010-05-13 20:33:30 by VladimirSlepnev:

Shrike from the Hyperion series by Dan Simmons fits your bill perfectly.

2010-05-14 04:05:00 by sunburstbasser:

Lightweight doesn't necessarily mean that a robot wouldn't be able to break through some kind of wall. Even with current metals and polymers we are capable of making materials far harder than the steel used for armor during most of the 20th century with less weight. A robot with a body made of such materials with the proper programming would be able to beat it's way through many barriers.

2010-05-14 04:40:03 by Solus:

Finally, more of the good stuff. I was getting tired of the programming junk you've mostly been posting recently. The sensor capabilities of the robot do seem to pose a problem, though. If its only method of knowing it must kill you is being able to see you, why not use active camoflage, temperature control suits, or if that tech is not available, even just disguise yourself as part of the environment? If the robot's not intelligent and can't learn, how can it tell you're not really a tree or a bear?

2010-05-14 05:01:12 by Brian:

Though this robot can kill very efficiently, its only defense is speed, and that's minimized. It has to run right up to a person to kill them, which is a restriction on its path, so you can either predict where it's going or know where it is (when it's killing somebody). Booby traps are probably the way to go, but you don't even need to use a magnetic field. Explosives and standard minefields should do fine. If your robot is made light enough to be that fast, it isn't going to have anything like armor, so a simple IED is likely to blow it to smithereens. Regular automatic weapons would probably work okay too, if you had enough of them. You aren't going to snipe the thing reliably, but when it's running at you and your buddies, you all open up with machine guns and fill the air with lead; you'll mostly miss but something will connect, and without armor it is unable to survive many hits. It would be seriously scary in a survival horror setting against a few people who lack significant weaponry. But I don't think they could depopulate a continent. Especially since, if there are large numbers of them, artillery and airstrikes become viable options.

2010-05-14 06:44:50 by RossSmith:

Or you could reverse the roles, and tell the story of the heroic lone robot using it's meager advantages of intelligence and speed to survive against the vast, terrifying human hordes :) "If there is ever a war between men and machines, it is easy to guess who will start it." - Arthur C Clarke

2010-05-14 20:37:19 by eneekmot:

@Thrack: Michael Crichton wrote Prey, about colonies of self-replicating airborne nanites. The swarms were actually a symbiote colony that would form small cameras, designed for spying. Much of the self-replication was done by bacteria. They could kill humans, not by eating them, but by suffocating them and causing severe infection and immune reaction (instant asthma.) I'd rather not spoil the details for you, though. Magnets were effective as a defense because the bots were metal, but the scientists found more creative ways to kill them.

2010-05-15 00:58:20 by pozorvlak:

Two words: area weapons.

2010-05-15 01:47:37 by MrUnimport:

I'm going to have to disagree with you there, Mr. Hughes. I assert that robots are fundamentally scary not for any such hIgh-minded reasons as unstoppability or murderousness, but are instead scary for the same reason that zombies are scary; that is, they represent the Human Who Is Not A Person. The Person Who Is Not A Human, in the form of talking animals, elves, aliens, etc. is by contrast a much friendlier face. The Human Who Is Not A Person terrifies not because it can't be reasoned with, but rather because it is incapable of comprehending reason. It trips all of our Uncanny Valley sensors, except robots don't even have to be human replicas to do so. They're not horrible because they bring death and can't be defended against, but rather because they represent death and insanity rolled up into one. The Thing in Human Shape is a primal fear, and making a robot faster, more powerful, and generally trying to engineer a more intimidating human-slicing machine does nothing to address this.

2010-05-15 19:19:19 by Daniel:

"Its electric battery - which can propel it at top speed through five carotid arteries per second for maybe a month and a half" What kind of battery is that? How about you kill one robot and they all die in a chain-reaction of battery explosions?

2010-05-17 03:28:29 by EDensity:

Fascinating thoughts. I definitely agree that the true strengths of robots are not often properly portrayed. And I too don't think that humans can create a human level AI, mainly because of my definitions of what information and intelligence are and what I see as the scientific laws governing them.

2010-05-17 16:03:34 by SkyTheMadboy:

Oh man, so many thoughts sparked by this. Zombies et al are fanciful, while robots actually exist. In a way, the monster robot is more akin to a serial killer - they're entirely possible, and while some are truly designed as monsters, others are capable of hiding in plain sight... just watching, and waiting, for an opportunity to kill. They may be outwardly normal, but on the inside they're insane - "wrong" in some subtle manner that makes them homicidal. For the record? I'm a LOT more scared of horror that features serial killers rather than murderous supernatural or extraterrestrial entities. I also just finished Portal this past weekend, which gives this topic a whole other shading for me. @RossSmith, darn you for giving me ideas.

2010-05-20 20:40:13 by Tekelili:

What kind of senses would these killer robots have? If they managed to give something like a sharks ability to detect muscle contractions at a distance we wouldnt even be able to blind the things with smoke grenades.

2010-05-20 21:06:22 by Graham:

@Telekili: I'm afraid that only works underwater. You'd be amazed at how bad air and dirt are at carrying electrical charges. The "extra senses" idea is interesting, however- you can very easily put thermal vision onto a robot and have it investigate anything near ~37 C. Anyway, my two cents: even with incredible speed, close-range weapons aren't always going to cut it (no pun intended). Unless your proposed robot can jump stupidly high, it could quite safely be bombed into oblivion, as other posters have mentioned. A non-ammo-constrained long-range weapon would be the best response to missiles and bombers. The immediate choice most Sci-Fi lovers would jump at is a laser, however, a lightweight anti-air laser is currently implausible, and will remain so until somebody invents a hyper-coolant of some sort. A better choice would be some sort of lightweight, "flexible" railgun, designed to load and fire small, nearby ferromagnetic objects. Another, less efficient choice would be to have the robot simply throw stuff at airborne targets.

2010-05-20 22:39:37 by Kirby:

Whose to say the robots don't shoot each other? They have no thinking, after all. And if they instantaneously shoot at anything that moves, that means that unless they're indestructible, lasers or missiles or whatever they shoot are shot at the same time, destroying each robot, just as if two people shot each other at the same time.

2010-05-22 17:41:33 by MrUnimport:

I should hope that whoever is programming these silent deadly assassin robots would be able to program them not to blow each other up.

2010-05-25 22:16:40 by db:

Natural selection is remarkably stupid, slow and inefficient compared to every other design method. Still natural selection can create human-level intelligence (it did). It's only a matter of resources.

2010-06-03 21:57:25 by kabu:

What just happened to half the website? Is it just me or are the only categories left there "fiction," "blog," and "meta?"

2010-06-03 22:04:33 by qntm:

Everything is still here, no links are broken, almost all content has been shoved under "Blog" for simplicity because I was tired of having everything spread out everywhere and grouped under arbitrary and relatively small categories. I've kept "Fiction" separate and that's about it for now.

2010-06-04 01:06:02 by kabu:

Oh, okay. I was worried there for a moment!

2010-06-04 05:01:55 by Thrack:

Hah, if you looked at my computer you would find I sometimes give a single file its own category (I expect to eventually add more in those cases though, it's just so I don't have to reorganize later). But everyone has their own way of course.

2010-06-10 23:02:47 by Wunderbear:

Looking at that video you posted. On the one hand, it's a clever yet troubling sign of the impending robot apocalypse. On the other, D'AWWWW IZZIWIZZUMS ISNTOOOCLEVER *robot does that climby-jumpy thing* EEEEEEEE! *claps hands* Really clever programming, and supremely cute. It doesn't hurt that it looks like a baby bat, as well.

2010-06-23 19:51:00 by Joseph:

Presumably, the robot would be able to avoid weapons easily. The moment it sights a weapon, it would get out of the way - it's not a question of how strong or accurate the weapon is, but rather a question of: Can you accurately aim at a robot going 150 kmph with special programming that lets it approach you while zigzagging at random intervals, making it totally unpredictable? In any case, I think some sort of flying drone with a machine gun would be more efficient. Every shot kills instantly, and it is fast and accurate enough to gun down a crowd of civilians a full auto without wasting a single bullet. But no, that would be a really dumb story. You'd just have everyone dead. I think your robot-determining questions are kind of hard. I tried i and -i for "the engineer's square root of minus one" before coming across plus or minus i. >_> I mean, something like "what color is a pear" would be easier. Wait, frig, plus or minus i isn't right either! Aaaaagh what is the answer

2010-06-23 19:51:47 by Joseph:

Okay, seriously, that question is really, really hard. I had to look everywhere for it, I finally found it on Wikipedia.

2010-06-23 20:36:59 by qntm:

A rudimentary ability to use Google and Wikipedia to find out information is a prerequisite of commenting on this site. Cheers :)

2010-11-21 21:37:48 by PhantomHoover:

Well, as far as killer robots go, the Culture's knife missiles are a fairly neat design: small, very fast, airborne and able to fly through heads with little to no resistance. While they're not going to sit well in a hard SF setting, the general principles are still applicable, and propelling something through the air very fast is already much easier than doing so on land.

2011-07-21 13:33:02 by Bob:

pingu is cooler than robots

2012-04-27 12:14:49 by oReallyLettersOnlyWTF:

(Forget the WTF part. It's there because I cannot but a question mark in there, so I had to fake the q-mark with letters.) Regarding fast, hard-to-kill robots. Railguns (or basically ALL kinds of extreme-v gun) work quite well on robots, esp. in air (while you'd still be better off keeping that stuff out of the 'barrel', mostly for similar reasons). Why? The projectile moves at several km/s if not tens of km/s. At that speed, replacing part of the slug with explosives is a bad move -- it lowers kinetic energy because the explosive head would be lighter than, say, steel. The added explosive yield would not make up for the loss of kinetic energy (either due to the reduction of moving mass, or the increase of drag if the explosive slug is larger). But there's more to it. While traveling towards the target, the projectile develops a plasma sheath, which will short a good deal of the chips on impact. And it'll pierce any light-weight armor with ease, while developing even more plasma. Armor alone is out. And the robot would not have much time to avoid the slug either, not one moving at 10km/s. It's far more plausible that the shooter will screw up than that the robot can actively move out of the trajectory in time. G limits and stuff. So speed alone (or combined with armor which don't slow it down to a crawl) is out, too. How to make the gun more reliable: add a tracking laser, not as a weapon but as a range finder. Modify the gun so that the trigger activates the laser, and if/when the range is suddenly found to decrease, (because the laser touches the robot rather than the terain around it) make the range finder trigger the actual gun. Ka-Pwn! One fried robot. (Of course, that implies that even an advanced AI cannot invent new weapons, and that Humanity has enough time to assemble a working railgun, after decades of procrastinating on government grants. The suddenly imminent lack of grants should be QUITE a good incentive tho.) I "hope" that your robot has a good deal of redundancy.

2013-02-15 23:41:10 by morganism:

Railgun firing expanding nets would be cool. Would interfere with the whips, and if it had a plasma field with a charge to short out the electronics, would be good visual. Carbon nanotubes are susceptible to sonics. unzips em. would be pretty cool on screen. I would also make em about waist high. Low center of gravity is good. small and dangerous is just extra creepy. a freind saw a chihuahua in Texas with rabies, and the thought still makes me want to go armed.

2020-05-19 11:50:10 by billdog:

150 mph doesn't feel like fast enough to be invisible. If you're quick with a shotgun you could probably hit one if you have good visibility. Failing that, thin wires strung across a field would probably go unnoticed and would trip one of these things up and destroy them, doors can hold them out indefinitely (unless they find a big window to smash) and the battery life will be pitiful.

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