Search the home for any openings larger than 1/4 inch. Pay particular attention to areas where food is stored. Inspect the areas around plumbing and electrical wiring, which are common points of entrance. Note smaller holes as well, since mice can chew on the surrounding material and enlarge the opening.
Tear off a sufficient amount of steel wool to completely fill the hole. Apply caulking compound to the steel wool. The addition of caulking compound creates a tighter bond with the wall, preventing mice from pulling out the wool.
Press the steel wool firmly into the hole. Add additional wool as needed until the hole is completely filled. Caulk around the hole.
Check the hole weekly for gnawing. Eating steel wool causes internal bleeding that will eventually kill the mouse. Should you notice that the steel wool has been gnawed, check the surrounding area for a dead mouse, and dispose of the body.