How can I tell if I have rodents in my walls during winter?

Sound is usually the first tip-off, and it carries real information: because rodents are nocturnal, scratching or scurrying concentrated after dark and localized to one section of wall or ceiling is a meaningfully different signal than random daytime noise. Extension guidance also directs attention to where mice exit walls rather than the wall itself -- along pipes, above drop ceilings, and on foundation sill plates -- because that's where droppings and grease marks accumulate even though the cavity interior never becomes visible.

A pet's behavior is an underrated sign. Dogs and cats can hear and smell activity a person can't detect, and repeated, specific attention to one wall spot -- not general curiosity -- often precedes a homeowner noticing anything themselves.

No inspection method available to a homeowner, and few available to a professional without invasive tools, lets anyone see through drywall. That means you cannot get a population count, a precise nest location, or confirmation of chewed wiring inside the cavity from sign alone -- and any source that claims otherwise from the outside is overselling what's actually knowable.

What you can do is treat the exit points as a monitoring station: place snap traps or non-toxic monitoring blocks along pipes, sill plates, and behind appliances, and check them every few days. A caught rodent, or bait activity, confirms the population is using that exit -- which is useful, real information, just not a full picture of what's behind the drywall.

Confirmed in-wall activity that persists despite trapping at the exit points, multiple walls showing sign at once, or activity you suspect has reached the attic or a wider void, are all past the point where sound and exit-point monitoring alone will resolve things. That's a fundamentally different job: locating the actual entry point from the exterior, and in some cases opening a section of wall or using a scope to confirm what's there -- work that requires tools and experience a homeowner typically doesn't have on hand.