My cats have alerted me to strangers coming out of the woods and walking through my neighbor’s yard. They are like watchdogs kind of, just quieter and you have to look and listen for their ques.
My cats also are great watchcats....from everything to bugs or outside people walking too close to the house. They hear things I can’t and when they perk up —I take notice and action. They also will surround a bug which gives me time to get the vacuum.