What is this

https://preview.redd.it/nngpbzygi7dg1.jpg?width=3072&format=pjpg&auto=webp&s=e92958a979f61f23bc5587d5c728488070a655dd

I came across this at the back of a closet when fixing my somewhat old (1950s) house. Tried pressing the button and nothing happened. But the switch was just like pressing a doorbell button.

Are there any Americans over here who can explain to a European migrant in their country what this is, and why it is in the back of a closet?