Legal to build a killer robot for home defense?

So, you can buy legal semiautomatic firearms. You can even put the ammo feeding them on a belt - magazines of any capacity limit are not actually required by law in most states.

Today, open source software exists for all kinds of things, including various forms of machine vision. All the servos and control boards needed are readily available from websites like Pololu and Sparkfun.

Full autonomy would be an extremely difficult challenge, but it’s at least plausible that a small group of hobbyists could hack something together that worked under limited conditions. I think a high end infrared camera and machine vision could possibly detect human sized “intruders” in a bounded area. IFF would have to be something like a strobe flashing at a particular frequency, or maybe a phone app and bluetooth or something.

Would it be legal to build a killer robot that would open fire automatically on intruders in an area? I mean, you’d be insane to give a cobbled together collection of circuit boards and servos live ammo…but would it be legal?

Also, the servo on the killbot that pulls the trigger can actuate the trigger very frequently. Would this be considered a machine gun…?


Answering the question as asked:
[li]To build? Who cares.[/li][li]To use? No because there is no direct threat against humans.[/li][/ul]

You can build almost any type of robot that you’d like. Where you’d run into problems are when:

[li]You attach a firearm to it - In the US, the BATF, the federal agency regulating firearms, has strict regulations about modifying firearms. If they were to inspect your completed “defense bot” and they it a category they call AOW ( any other weapon meaning that the weapon has been illegally modified without the proper taxes being paid) you would have to pay the tax or disassemble the weapon . Otherwise you’d face criminal penalties.[/li][li]Creating lethal booby traps - Almost no municipality in the US will allow you to guard your property using a booby trap which can kill an intruder. Even maiming someone could get you into hot water. This is because there has to be a imminent and perceived threat to life to use deadly force in most areas (the autonomous nature of the booby trap makes this impossible to justify) and there’s the very real threat that a first responder could be injured or killed by your device.[/li][/ol]

Killer robots are a bad idea all the around.

IANAL. However, you have two obvious legal problems:

  1. I don’t see how a robot is substantially different from a deadly trap, which is illegal in virtually all jurisdictions.

  2. Law generally allows you to use deadly force to defend your own life or the lives of others. It generally does not allow you to use deadly force to solely protect physical property. A killer robot designed to kill intruders when you’re not there is obviously meant to defend your property, not your life.

If mounting a gun and pulling a trigger without human interaction was illegal, then The Mythbusters would be done for that already.

Perhaps the best solution is to make something regulations don’t apply to, if it is a rail gun I doubt you will find anything applies legally.

Of course you can get in trouble for endangering people is it was a problem.

Obscure the weapon and until it shoots someone there is no problem likely to occur.
Once it shoots someone it will be a problem whatever the law has to say about it otherwise.

And even defence of life thing will likely see it go to court and the verdicts do not always go in the direction of good sense.

Programs like MythBusters work with licensed FFL Class II dealers/armorers who own the weapons that they use and through whom they can pay the appropriate taxes for modifying firearms. Television productions do not own firearms for legal and insurance reasons.

And rail guns are actually covered by BATF regulations as are directed energy weapons. While neither of these are widely available, it was clear by the 1980s that they would be in the coming decades and regulations where put into place to control their distribution and sale,


Obligatory link to the South Korean Samsung killer robots in the DMZ: However, it needs a soldier to give the final “OK” for it to go Robocop on somebody.

In what episode did they ever make an autonomous gun? Sure they do remote control all the time (usually with a string, sometimes an electric motor) but that is still completely human-controlled.

is this just going to open first or will it say “search, destroy, kill” first?

You have 20 seconds to comply!

In England these would probably count as spring-guns, purposed against poachers, burglars and radicals until they were banned nearly two centuries ago. That is if they were left unattended — were one to attend them, one might as well just sit there swathed in bed-clothes, waiting for imagined miscreants, nursing a rifle on one’s knees, muttering to oneself.
I have no idea if other countries have 19th century laws against spring-guns.

Of course, there is a solution to the spring-gun/lethal booby-trap issue: build a sentient armed robot, such that the finished device is more akin, legally, to am armed guard than a spring-gun.

Reasons that this is a terrible idea are left as an exercise for the reader.

I thought up this question when I thought about the scariest possible system to engineer. Flying in an airplane you helped design or riding in a car with code you helped write is one thing. But giving live ammunition to a robot you built that is programmed to fire at anyone who meets certain parameters…I can’t think of anything scarier.

Giving it sentience just makes the problem worse (if you could do such a thing). A sentient machine can learn and to an extent adjust it’s own programming.

which is why I have hardwood floors instead of carpeting.

If you build a robot with a cradle to rest a firearm in and a mechanism to pull the trigger, and nothing is attached, could that reasonably be construed as “modifying a firearm”?

The cradle may be consider to a “stock” and adding a stock to a pistol makes it an short-barreled rifle in the eyes of BATF. It would be legal if you pay the tax and have it approved by the BATF.

However, since it’s a booby trap device and would be illegal under local laws, it would almost certainly be denied by them.


Most are assuming that the robot would be considered a lethal trap, but I don’t think that’s a given.

If I were to build such a robot and only activate it when I was personally present and felt my life was in danger, what then? Presumably, making a robot that aims better than I do when I’m scared and it’s dark and I just woke up (for example) is within the reaches of current engineering, so it would be a reasonable thing to do for someone who wanted to keep a gun for home defense. It could also potentially do a much better job of identifying known members of the household, so it could reduce the chance of an accidental death as well.

Umm, You are still in a very dangerous area, but SOME states – My state of Mississippi is one of them – DOES allow for the use of deadly force to protect your property - Check your states “Castle law.”. So there is a chance, that you could “open fire” on someone who is committing “mayhem” on you property - but I DON’T recommend it! You would need an EXTREMELY lenient sheriff…

Now, the use of high velocity paint balls or “cattle prods” is always an option - because the intention would be “deterrence” not “death,” Kinda like a barb-wire fence. an electric fence or a pit bull. Paint balls may not be deadly, but they are annoying as hell after about 100 of them…

Localities are becoming more and more “intolerant” of crime, so I can see a day where a drone/droid that is DIRECTLY UNDER YOUR CONTROL will be allowed to open fire on a burglar/vandal, as long as the video and other evidence shows they were unwilling to leave “peacefully.”

But as of today, unless you or your family is in the house, the “autonomous drone” will be very hard to defend in court… BUT IF YOU/ANYONE is at home, it is just “self-defence” like any other weapon…

What about a Sheldon Cooper-style virtual reality bot? Seems to me that if you went into your safe room, put your VR headset on, and fired up your combat bot to go clear your house, that might be less sketchy than having some kind of homebrew ED-209 roaming your house at night.