They are most effective within 20 yards, but some can reach out pretty far.An excellent camera for the price is a moultrie d40 ($99)..As far as night time pictures go, the flash can only reach so far, and there are also IR cameras. I'm usually not too worried about my cams getting stolen because my family owns the farm I hunt on and we're surrounded by people we trust that keep an eye on our property. But as yours are for security purposesI understand your concern. Ive never thought to use a game camera to catch humans..very innovative, haha.

All I could say it try to keep it brushed in some what but with a clear lane for the lens to still capture good pics. And like Mottz said, you could try hanging them higher, angled downward. People have a tendency to not look up in search of stealing things, unless its a treestand that sticks out or something.