Some people think that if their house is in "the big city" there is less chance for mice to bother the house. Not true. They are around, and when it's cold they will want to get in. It's best not to provide them a mouse highway!
A mouse only needs a space 1/4" wide to get in! That's it. And they are always looking for those spaces.
Electricity needs to get inside the house.
Large service conductors bring it in.
They need a large hole on the side of the house.
And that hole is typically filled with some form of putty, or a large clamp.
In this house, one block from the United States Capitol Building, the electrical service was upgraded at some point in the past, to a 200amp service.
That required a larger conductor than existed prior.
Outside there was a large gap present.
Inside there is a large gap between the wall and the panel box.
And there is a large gap on the side of the panel box, never sealed!
This is a mouse highway!
So it was not surprising at all when we found evidence of mouse infestation in a house that has been empty for some time.
My recommendation: it doesn't hurt to walk around the house and look for possible mouse entrances - the electrical connection, where the AC line(s) enters the house, where data lines connect, etc. You might be surprised at what you find! Before you put in any putty or other sealer, take a Brillo pad or some other steel wool and put it in the hole first. Rodents will not try to chew through steel wool.