I grew up in a house built in the 50s. Even though backyards were mostly private, they were still built with a two-chime bell. One chime for the front door and one for the rear door. While the power meter guy would, of course, go into backyards unannounced to read the meter, I still don't know why that would have been a normal thing for people to go into back yards for it to need a separate bell button.