Bella is a little protector also. We had some really windy days, and it would blow the front door and it sounded like someone was coming in, and she started barking and running towards the door and then back into the livingroom...or when shes outside she will see kids or other dogs and she barks all brave and then runs as fast as she can up on the porch...LOL
She has also gotten to where she can tell whether or not its us or someone else coming to the door. She doesnt bark at us when we approach the door, she just goes nuts when we get in, but when we get company she knows they are there before they ring the door bell.