Sofie isn't shutzhund trained, but Yann is (not titled, but he trained alongside his brother who is), and they both react similarly and intuitively to strangers. They come to attention around the man with hunched shoulders and darting eyes, but greet the next guy, though dressed similarly shaking my hand with wagging tails. I understand accidents happen, but I think for the most part most trained dogs will be able to easily distinguish the perp.
When we adopted Yann, he was trained to mostly the same German commands we trained Sofie to. But it took probably a couple weeks at least before he actually took us seriously as his leader. Sofie snaps at my every command, but is sluggish with it when my husband is alone with her, because he doesn't work with her as much. I VERY seriously doubt just any random stranger, especially one breaking into our home.
And my dogs aren't seriously trained, either (well, Yann isn't anymore). I imagine a true schutzhund dog would do better.
Sofie Rose born 08/2012
Yann von Erzengel born 02/2006