I am on the second floor of an old house in the northeast USA. There is another one at the entrance to the second floor, this at the backdoor. The button looks like a bell but what is the hole for?
Here are some of the answers:
1. One of them said: Honestly you might be able to speak into it and hear whoever is at your door when they speak back
3. Other response was: Perhaps just another eyehole or peephole. Like a handicapped accessible hole.