Full answer
Mice almost always enter through gaps smaller than you'd expect — a hole the size of a dime is enough. Before setting any traps, do a perimeter inspection of your home and seal every crack, gap around pipes, and unsealed vent with steel wool stuffed in first, then covered with expanding foam or caulk. This is the only permanent fix; trapping without exclusion is an endless cycle.
Snap traps remain the most effective and humane quick-kill option available. Bait them with a small dab of peanut butter pressed onto the trigger — far more attractive to mice than cheese. Place traps perpendicular to walls (not parallel) with the trigger end touching the baseboard, since mice run along walls and will step directly on the trigger.
Set multiple traps in clusters of 2 to 3 in areas where you see droppings or grease marks on walls. Mice are naturally curious and will investigate new objects in their territory within the first night or two. Check traps daily and reset immediately after a catch — fresh scent from other mice can actually attract more to the same spot.
After the infestation is cleared, maintain prevention with proper food storage (sealed containers, not bags), routine cleaning under appliances and behind cabinets where crumbs accumulate, and keeping outdoor entry points like firewood stacks and dense shrubs away from the home foundation. A single breeding pair can produce 50 to 60 offspring per year, so early action matters enormously.