> If I lived in a rural area, I would also want a drone to take off half a mile away and film people coming to my house. That way I'd know who's coming and have a record of it even if they thought they destroyed all the surveillance video.

I use security cameras strapped to the top of very high trees on my property, triggered by motion detection. Keep it simple. (Suburbs of a major city in Central Florida)

As a bonus you get a cool perspective-shift in the images as the trees slowly grow ;-)

Unfortunately that's a legal minefield. Mantraps have various legal standing around the world, but you are likely to be successfully sued if they result in injury. Seems likely in the case of a panicky criminal who finds themselves suddenly boxed in with mysterious gas.

There are other considerations as well (via wikipedia [1]) : "There is also the possibility that such traps could endanger emergency service personnel such as firefighters who must forcefully enter such buildings during emergencies. As noted in the important US court case of Katko v. Briney, "the law has always placed a higher value upon human safety than upon mere rights of property"

[1] https://en.wikipedia.org/wiki/Mantrap_(snare)

I am pretty sure that a criminal who trespasses on a property that clearly says "private property" has no standing to sue you for what befalls them on your property. Within reason, of course.

That is why private islands have those signs - otherwise someone coming ashore could assume it is a regular public island.

I believe there is a British(?) system that works like this: A sound wavefront generating bar + stroboscope mounted above the door(s) plus fog dispensed from some chemical container.

I'd hate to be the first family member to accidentally set off that system

Maybe you'd love it :)

Now you're talkin'. True security theatre.

I would also add a laser that slowly scans the room, combined with the voice from the first Resident Evil movie.

Would you get sued for him tripping over your coffee table because of the fog or my lasers?

In a rural area, they would just shoot the drone (I still really like your idea). You could blanket the area with inexpensive trail cams.

Who would notice a small drone that far away? It would zoom in as they approach the door. You are right - a few drones is better.

I bet the folks at /r/homeautomation could work up something for this :)