The boabs come with the building. Their fee is part of your rent, more or less. In addition to just being a watch dog, they also wash your car, carry your groceries, and pretty much any other task (when our car got here, one of them rode with us to an auto parts store to negotiate tire prices).
There's an MB official in my building, so we also have armed guards. But when things get bad, the boabs lock crap down on their block. And they know every face and every vehicle that belongs. A strange face or a even a bus that comes at an odd time are a no go. And by "armed," I mean maybe a few small handguns but mostly clubs, knives, etc.
Doubt it would work in the US. Prolly too expensive. There's probably something similar out there already.
