Had the same problem in our home. Of course it usually happened in the middle ofthe night!
Replaced the batteries a couple of times. I then called the manufacturer. The first question they asked is what type of batteries I was using. They said that Duracell and Everyready alkaline were ok to use but they advised not using Rayovac.
They then asked the manufacturing date. It was just over 5 years. They advised me that it had reached it's "end of life."
I wanted to replace it with the identical one because the base was already installed and if I used another brand I'd have to repaint. I found the one you're dealing with at the hardware store in the plaza near the Villages Golf Cart Store on rt.441. I believe it was an Ace or True Value hardware store.