The mice aren't inside the house itself (not anymore - several handymen later) but they are getting inside the walls of the house. I've put poison in the crawlspace under the house (probably need to put fresh now that I think of it) and inside the door to the plumbing by the tub in the bathroom. I've paid handymen in the past to plug up holes around the house and try to exclude them with wire mesh and close-fitting crawlspace doors. But they are somehow finding more ways under the house, then they go up into the inside of the walls. I don't know how to find the little spaces they must be using to get under the house. And the bottom of the house is covered by insulation and plastic (moisture barrier I think it is), so I have no idea where they sneak in. I wonder if there is any practical way to figure it out?
Now that I think of it, years ago when the problem wasn't happening we had several barn cats and the crawlspace was accessible to the cats. But, I don't want to go back to having barn cats because now I have a nice variety of bird-life outside, and I feel too old to mess with any barn chores, not even cats. I feel so old, and I'm still 2 years away from full retirement age, but I am seriously thinking to retire a year early (next year, as soon as there is a covid-19 vaccine).