Note: this post has descriptions of killing rodents.
We had numerous mouse issues in our previous apartments. Here's what helped me:
1: reduce their reason to get inside. Seal up dry goods in jars, make sure counters and floor are clean of food bits and also dry - they will visit around the sink to drink water.
2: make outside seem like a better choice. Is there a woodpile or some other appealing habitat mice could go instead? Is a cat or terrier an option?
3: remove the ones that do show up. I opted for lethal traps rather than catch and release. I didn't have as much luck with snap-traps, so i made up one. It was single-use only before resetting, but remarkably effective, though a little on the grim side.
Supplies: Semi-rigid plastic bag, like a pretzel or crisp bag. Large trash can. peanut butter. water. scissors.
Fill trashcan about 1/3rd to halfway full. This can was about twice the height of a 5gal bucket.
Take the plastic bag and cut the two bottom corners off at a diagonal. This is to allow water into the bag.
Small dab of peanut butter goes in the bottom of the bag. Bag is balanced halfway off the countertop, positioned over the trashcan, before you go to bed.
Either my partner or I would hear the bag rustling and then fall into the can. I would get up, go in the kitchen and kill the mouse as quickly as possible. The water is there as a failsafe; the first version of the trap didn't have water in the bucket, and when I came out to the kitchen, the mouse was jumping around frantically before it was dispatched. Falling into water is no treat either, but at least that way if you don't hear the trap, the mouse will drown.
If the idea of executing the mouse by hand is troublesome, remove the bag and pour water+mouse down the toilet. We only did that once or twice; each time the quantity of water was sufficient to send the rodent down the drain.
This trap is my adaptation of what my dad told me they used to do to get rid of rats in the barn when he was growing up: something similar to
this method
I had a remarkably high success rate with this method; the only thing that was comparable was glue traps, which I really don't like to use. When we used glue traps, I would make sure the mouse was dead before tossing the trap, but that still meant the mouse was stuck there all day until I checked the trap. A friend has seen people pick up a glue trap, mouse still alive but adhered, and toss it in the trash. That's downright cruel, if you ask me.