What should I look for in homes to catch winter pest activity early?

Rodents seek winter shelter inside buildings following the first sustained cold spell each fall, which means the weeks immediately before and during that cold snap are when a home is most attractive to an animal deciding where to spend the winter, and also the window where an inspection catches the fewest established problems and the most open opportunities. Checking entry points and storage zones during this window is true early detection, not a generic "do this sometime" recommendation.

The entry-gap numbers matter here specifically because they turn "look for pests" into "look for these openings": mice need only about 1/4 inch, roughly the width of a pencil, and rats need about 1/2 inch, roughly the size of a nickel to a half-dollar. Finding and sealing a gap that size before the cold snap is functionally the same as preventing the infestation rather than detecting it after the fact.

Foundation gaps and utility penetrations are where the entry actually happens, so they come first on any early-detection checklist. Door sweeps and worn weatherstripping are the next most common gap, since these wear down gradually and often go unnoticed until a cold draft or a gnaw mark calls attention to them.

Attics, basements, and crawl spaces are the shelter zones once an animal is inside, and pantry or garage storage areas are where food and nesting material concentrate. Checking all four categories, rather than just one, covers both the entry side and the harborage side of the same problem.

It would be easy to read a thorough walk-through as a guarantee, and that's not accurate. You can inspect the surfaces and openings you can reach, but you cannot see inside wall cavities, under a slab, or into every inaccessible soffit void -- so early inspection reduces risk substantially without eliminating it entirely. Admitting that limit up front is what makes the rest of this checklist trustworthy rather than a sales pitch dressed as a safety guarantee.