Mice do not hibernate. They move in. Sometime in the fall, when the first cold night hits, they start looking for a warm wall and a crack the size of a pencil.

That is the number that surprises people. A mouse fits through a gap the width of a pencil. Not a hole you would notice, a gap you would walk past a hundred times.

Walk the outside first

Start at the foundation and work up. Look where pipes and wires enter the house, where the siding meets the foundation, and around every window and door frame.

1. Fill small gaps with copper mesh, not steel wool. Steel wool rusts and mice eventually chew through it.
2. Seal over the mesh with exterior caulk.
3. Check the garage door bottom seal and replace it if it is torn.
4. Look at the dryer vent flap. If it does not close flat, that is an open door.

Then the inside

Check under the kitchen sink where pipes pass through the cabinet floor. Check the gap behind the stove. Check the basement rim joist area if you have one.

Anywhere a pipe goes through a wall is a candidate. That is the most common entry point by a wide margin.

Remove the invitation

Mice come for warmth and food. Firewood stacked against the house is a bridge. Bird seed in a garage is a buffet. Fallen fruit under a tree is a dinner bell.

Move firewood 20 feet from the foundation. Store seed in a sealed bin. Clean up what falls.

Signs you already have them

Droppings along walls, not in the open. Greasy rub marks where they travel. A faint ammonia smell in a closed cabinet.

If you find those, set traps along the wall, not in the middle of the room. Mice run along edges, and a trap in open space catches nothing but your toe.

One weekend of sealing beats a winter of listening to scratching in the ceiling at 2 am.