When it gets cold outside, mice are no different from humans in that they want to come in and get warm, too. If that were not enough, mice also enjoy many of the same foods that humans do. Once they find a way into your home, they can expose you to Salmonella and other diseases. They urinate and defecate prodigiously in and near your food supplies. They gnaw through almost everything, including electrical wires. They cause expensive property damage, including risk of electrical fire. Keep them out.
Buy a new garage threshold every 2 or 3 years. A garage threshold is a strip of rubber that is glued to the ground where the bottom of the garage door touches.
Garage doors must seal completely at the base; mice need only 6 mm (1/4 inch) of space to squeeze through.
Lay the sealing threshold according to manufacturer's directions. The threshold must sit securely against both sides of the garage door. If the threshold is not long enough, mice will enter at the corners. After laying the threshold, close the garage door. Inspect to make sure that there is no light shining between the floor and bottom of garage door.
Install metal flashing on the bottom and sides of wooden garage doors. Door flashing covers the edges of the door so the mice will not gnaw through the wood. The sealing threshold applied to the ground prevents the metal flashing from constant contact with cement and water.
Inspect the interior of the garage. Cracks and holes in the walls or floors can be used by mice to enter. Stuff these holes and cracks with copper mesh, steel wool, or patching compound mixed with steel wool.
Inspect the perimeter of the garage's foundation for places mice can enter. Stuff holes with copper mesh; copper will not rust but steel wool eventually will. For best mouse exclusion, mix concrete with copper mesh or steel wool, and use it to patch up holes and cracks in the foundation.
Any food stored in the garage must be kept in sealed containers. Use plastic containers for dry storage.