I’m sure you’ve seen them… 6’ chain-link fences with a relatively short (15" or so) barbed-wire section on top.
The barbed-wire section is usually angled. I assume this is done to make it more difficult for someone to traverse over the fence. But I would guess the difficulty of traversing the fence would depend on the direction of the angle relative to the person; if the barbed-wire section were angled toward the person, it would be much more difficult to traverse.
With this in mind, I would think a building would always angle the barbed-wire section away from the structure it is protecting. That way, it keeps people out. Yet I see many buildings with the barbed-wire section angled in. It looks like they’re trying to keep people in! Why do they do this? Did the fence installer screw up?
Yes, angle-out is the best option, for intruder prevention.
However, this may encroach on land that is not yours. Even being over land can be enough, depending on local regulations, even if you don’t touch the ground. And anything from an angry neighbour to a serious tresspass allegation could result. Plus if somebody hurt themselves on it, and then wanted to sue, could you imagine the legal wrangles?
Far better to take the second-best option and point the stuff inwards.
And there’s also cases where you’re trying to keep people in: Jails, prisons, mental hospitals, that secret facility where they hold captured alien lifeforms, etc.
That’s how you tell what kind of building it is - if they want to keep people in or out.
Also, it can be just as hard to go over a fence that has a thing that goes away from you, if you think about it. If the fence is tall enough that you don’t want to just drop down.
I think maybe it is to keep people in. The intruder can scale the fence the “easy” way on the way in, but when he’s trying to get out with an armful of stolen stuff, ihe’s faced with the more difficult approach.
Exactly what I was thinking, TheLoadedDog. It’s like the banks in the Harry Potter books. (minor spoiler) IIRC, you can get in just by touching the wall, but after that, you can’t get back out unless an employee happens to open that vault, which might be long after you’ve died, sitting inside there, wishing you’d chosen a more successful career than “wizarding bank robber”.