There is a gated community in Florida actually named "The Cloisters". It has a guard house at the gate and it is surrounded by a concrete wall. You might expect this to be in a terrible city, but no! It's probably in one of the safest places in the whole state.

That's a bit over the top, but it is useful to able to quickly identify people with no good reason to be in the neighborhood. People can go their whole life without mugging or burglary.