I have a beagle, and she barks through the door at other dogs or people walking past, mostly saying "Mommy, why won't they come play with me?"
If she is outside and barking, you can guarantee, the neighbors labs, dachsunds, cockers, chow-gsd mix, or whatever other breeds people in this neighborhood own are barking too.
The only time my beagle barks when other dogs are not barking too is like I said when she sees another dog or person walking by the house that she wants to play with.