Short answer: repellents rarely solve a rodent problem. University of California IPM's pest notes say rats and mice quickly get used to repeated sounds, that ultrasonic devices have very limited use, and that no repellents have been found to solve a rat problem for more than a very short time. Scents and sprays may make a spot less attractive for a little while, but rodents with a reason to be there, such as food, warmth or a nest, come back.
That does not mean you have no options. It means the money is better spent on sealing, sanitation and traps. Here is what the research says about the common products, and what to do instead.
Ultrasonic devices
Plug-in ultrasonic repellers are the best-selling repellent and the most disappointing. UC IPM's house mouse pest note explains why: ultrasonic sounds are directional, do not penetrate behind objects and lose intensity quickly with distance. It adds that there is little evidence sound, magnetic or vibration devices of any kind will force established house mice or rats out of buildings or provide prevention or control.
Its rat pest note says rats are easily frightened by unfamiliar noises but quickly get used to repeated sounds, making high-frequency and ultrasonic devices ineffective for controlling rats in homes and gardens.
In a Richmond house with mice in the walls and crawl space, a device in the kitchen outlet cannot reach the places the mice live.
Peppermint oil, mothballs and other scents
Strong smells may make rodents avoid a spot briefly. UC IPM notes rats have an initial aversion to some odors and tastes, but no repellents have been found to solve a rat problem for more than a very short time.
Mothballs deserve a warning. They are pesticides with label directions, and Virginia law makes it unlawful to use a pesticide in a manner inconsistent with its labeling. Read the label before putting them anywhere, and keep in mind that fumes from a crawl space or attic can reach living spaces.
Want a provider to look at it?
Describe what you are seeing and where. The call is free and goes to an independent rodent control provider who serves Richmond and the nearby counties.
Predators and pets
Cats and some dogs catch mice and rats. UC IPM says there are few situations in which they control rodent populations well enough. A cat may catch the occasional mouse in the kitchen while dozens live in the crawl space. Pet food left out can also feed the rodents you are trying to remove.
What works instead
The CDC's approach to rodents is to seal up, trap up and clean up. For a Richmond home, that looks like this:
- Seal entry points. Mice need a gap only about 1/4 inch wide according to the CDC; rats need about 1/2 inch according to UNL extension. Seal with steel wool or copper mesh and sealant for small holes and metal, mortar or hardware cloth for larger ones. See exclusion.
- Remove food and shelter. Seal pantry food, put away pet food at night, move bird feeders and compost away from the house, and keep supercan lids closed.
- Trap. Snap traps along walls where you see signs. See our traps article.
- Clean up. Use the CDC's wet method for droppings, so you can tell if new activity appears.
Is there any place for repellents?
Some homeowners use a repellent product in a car engine bay or a stored boat as one extra layer. That is a reasonable small experiment, as long as you do not rely on it and you follow the product label. Check the car or boat often for droppings and nesting material either way. If you hear or see rodents, treat it as a rodent problem, not a repellent problem. For cars, UC IPM suggests a weighted car cover that seals to the ground, along with rodent control around the property; our car and garage article covers it.
Ask before you pay for repellent service
If a company offers a repellent treatment as the main solution, ask what evidence supports it and what happens if rodents stay. Virginia's pesticide law lets the state board act against licensees that make false or fraudulent claims misrepresenting the effect of materials or methods. A good provider will talk about sealing, sanitation and trapping first, and can show you the gaps that need closing. Our inspection page explains what that visit should cover.
Call a local rodent provider
The call is free. Describe the problem, ask what the visit includes, and get a written price before any work starts.
Questions people ask
Do ultrasonic pest repellers work on mice?
UC IPM says ultrasonic sounds have very limited use because they do not penetrate behind objects and lose intensity quickly, and there is little evidence they force out established mice or rats.
Does peppermint oil keep mice away?
Strong scents may deter rodents briefly, but UC IPM says no repellents have been found to solve a rat problem for more than a very short time.
Can I use mothballs in my crawl space for mice?
Mothballs are pesticides, and using any pesticide in a way its label does not allow is unlawful in Virginia. Check the label, and remember that fumes can reach living spaces.
What is the best way to keep mice out?
Seal gaps of 1/4 inch and larger with materials mice cannot chew, remove food sources and trap any mice already inside.
Will a cat keep mice away?
A cat may catch some mice, but UC IPM says there are few situations where predators control rodent populations well enough. Sealing and trapping still matter.