I think my little girls would bark and that's about it. They might aggravate the bad guy by barking a lot & they might lick him/her into submission . Sissy has this high pitched voice--rather irritating after awhile. LilGirl's voice is not as shrill. When Annie barks outside, the girls are a double echo. It gets crazy when all three are barking. What would Annie do? Hmmm, I think she would go far away from the person and she might bark, not sure. Unfortunately crooks dont have to worry about my dogs.