They'd definitely bark if someone came to the door or tried to get inside. I really doubt they'd do anything once they got in. Probably go for attention My last Lab, Josie, may have attacked. She was very protective of me and even just certain men walking up to me outside would get her barking. A drunk man approached me once late at night and he scared me and kept asking to see Josie. I said no she's not friendly. (not thinking she'd do anything but the guy was creepy) Anyway the guy said he didn't care and came up to me anyway and she started barking and even snapped at him when he got too close. He immediately backed off and went a different way. I was thankful for that. That was the only time she ever snapped though.