Maybe you hear a rustling in your dog's food dish. Or spot droppings in the cabinet under the sink. Or come face to face with a mouse itself.
Besides the yuck factor, mice in the home pose a health risk, said Stuart Nichol of the Centers for Disease Control and Prevention.
"We strongly encourage people at this time (of year) to rodent-proof their houses and try to prevent the rodents from coming in in the first place," said Nichol, chief of the CDC's Viral Special Pathogens branch.
As the weather turns colder, mice are "looking for a little bit of warmth" and a way to get inside, said Missy Henriksen, spokeswoman for the National Pest Management Association.
All they need is the smallest of holes, as small as a coin, to gain entry.
So a first step in pest management is inspecting your home for possible entry points.
Have the screens on the chimney, attic or dryer vents detached? Is the weather stripping around doors or windows worn? Has the putty come loose around air conditioning hoses, or where the electricity or cable wires go into the house? Is there shrubbery close to the house or ivy around the foundation and up the outside walls that mice can use to hide or climb?
"The most effective means of pest control is controlling the problem before it becomes a problem," Henriksen said.
Pest control technician Shane Flanagan usually starts with a visual inspection of the property to try to see where mice are getting in and where they might be nesting. He'll look in the kitchen and unfinished areas of the basement and attics. "All that insulation is perfect nesting for mice and (other) rodents," said Flanagan, who works for PestNow, based in Sterling, Va.
Then he sets traps. Placement is key: Mice run along walls.
"If you put them in areas where they're running, you'll catch them," said Flanagan.
For do-it-yourselfers, there are many kinds of traps available. There are the "old-school snap traps," as Flanagan calls them; peanut butter works as an effective bait. For the more squeamish, there are snap traps in a plastic housing, so you don't actually see the mouse when it's caught. You can also purchase electronic traps and glue traps.
Flanagan uses snap traps. When he returns to check them, "That gives me more of an idea of the population, how many we might have."
After removing any dead mice from the traps, he'll set up bait stations inside and out to try to prevent further infestations. He'll also try to seal up areas where he thinks mice are getting in and around the house. That might include putting copper mesh along the dishwasher line, a frequent way that mice get into the kitchen.
And he'll recommend that homeowners remove shrubbery or ivy close to the foundation, pulling it back at least 15 feet from the structure.
The CDC also recommends picking up pet food and water bowls overnight, using thick plastic or metal containers to store grains and pet food, and placing bird feeders some distance from the house.
"Pest control is based on science, not magic; remove the conducive condition, reduce the population and maintain it," Flanagan said.
Many pest control experts recommend against starting with bait stations. Dead, decaying mice can leave an odour, so it's important to know where they are so you can get rid of them.
Mice left unchecked can cause problems by chewing on electrical wiring and insulation.
In addition, the CDC says mice and rats spread more than 35 different diseases globally.
Nichol said hantavirus pulmonary syndrome and lymphocytic choriomeningitis virus (LCMV), two viruses carried by mice, are associated with "particularly severe diseases." LCMV poses a particular risk to pregnant women because it can cause congenital defects in the fetus, he said.
"You don't have to have direct contact with the mice to get an infection," he said. "You can get it just from the droppings or the contaminated dust."
Safely dispose of any mice caught, and disinfect the areas where they've been. A bleach solution or Lysol-like spray works well, Nichol said.
"We all know whether we have in the past had rodent problems," he said. "If you've had that problem, get out ahead of it."