How mice enter your home: A mouse can squeeze through a gap the size of a dime (about 6mm). Common entry points include gaps around utility pipes, foundation cracks, gaps under doors, unsealed vents, and openings around HVAC systems. 

The exclusion method (the permanent fix): 

Walk the exterior of your home systematically. Use steel wool stuffed into gaps around pipes — mice can’t chew through it. Seal over the steel wool with expanding foam or caulk. Add metal mesh (hardware cloth with ¼-inch openings) over vents and larger openings. Install door sweeps on all exterior doors. 

Trapping indoors: 

Snap traps remain the most effective and humane method for killing mice. 

Place them perpendicular to the wall where you see signs of activity (droppings, gnaw marks, rub stains). 

Pre-bait by leaving an unset trap with peanut butter or chocolate for 24 hours to let mice get comfortable with it. Then set the trap. Check every 48 hours and dispose of catches wearing gloves. 

Place at least 6–10 traps — homeowners consistently underestimate how many are needed. A common mistake is placing two traps and expecting to catch every mouse in the house. 

What about poison bait? Rodenticides are effective but carry risks — dead rodents can poison predators (hawks, owls, foxes) through secondary poisoning, and a poisoned mouse may die inside a wall, creating odor problems. Use only as a last resort and always in tamper-resistant bait stations. 

Ultrasonic repellers: Products emitting high-frequency sound waves are marketed as mouse deterrents. Studies show mixed results — they may help prevent mice from establishing in treated rooms but are ineffective against an existing infestation. Best used as a supplemental tool alongside exclusion and trapping.