Most rodent repellents don't work well enough to solve a rat or mouse problem. Cornell's New York State IPM program says scientific evaluations of ultrasonic devices have found no effect on target pests, and a University of Arizona Extension column says that when ultrasonic devices were placed in rat-infested attics, the populations kept living and reproducing there. Scent repellents like peppermint oil have even less evidence behind them.
What does work is the boring part: removing food, trapping and sealing the openings.
Ultrasonic plug-in devices
Ultrasonic repellers plug into an outlet and emit high-frequency sound that is supposed to scare rodents away. The research hasn't supported that.
Cornell's NYS IPM program says scientific evaluations of ultrasonic devices have found no effect on target pests, and that the frequency and intensity manufacturers claim don't match the actual output. It also warns that some devices exceed OSHA limits for human sound exposure.
The University of Arizona Extension column says that in caged tests animals placed beside these devices continued to live normally and reproduce. It also notes that the Federal Trade Commission charged several companies with false advertising in the 1980s.
Sound also doesn't travel through walls, furniture or insulation, so even a working device couldn't reach rodents in a wall cavity or an attic.
Peppermint oil and other scents
Peppermint oil, cayenne, cloves and other strong scents are popular home remedies. Rodents may avoid a strong smell for a short time, but scents fade quickly, especially in Jacksonville heat and humidity, and rodents get used to them when food and shelter are nearby. There is little research showing these scents get rodents out of a house.
They are pleasant and mostly harmless, but treat them as a supplement at best.
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(904) 593-1371Tap to callMothballs
Mothballs are a pesticide registered for clothes moths in sealed containers. Using them in attics, gardens or engine bays isn't what the label allows, and the fumes are a health concern for people and pets. They are not a rodent control method.
Repellent sprays and granules
Some commercial sprays and granules use bitter or spicy ingredients to make surfaces unpleasant to chew. They may reduce gnawing on a specific item for a while, such as wiring in an engine bay. They don't remove a population, and rain and heat wear them off quickly outdoors.
Predators and pets
Cats catch some mice, and barn owls and hawks hunt rats in the open. Neither reliably clears rodents from an attic or wall, and a cat that hunts outside can bring disease and parasites home. UF/IFAS warns that rodenticide placed where wildlife can reach it is illegal, partly because owls and hawks can eat poisoned rodents.
Why repellents are popular anyway
Repellents sell well because they promise an easy fix with no dead rodents to handle. They also sometimes seem to work, for a reason that has little to do with the product: people who buy a repellent often also clean up, put food away and close a door or two, and that does help. Rodent activity also rises and falls on its own with weather and season.
If you already own a plug-in device or a spray, there is no harm in leaving it in place, as long as you don't rely on it. Do the things that work alongside it: seal gaps, remove food and trap. If the noise stops, it was most likely the sealing and the traps.
For the car and garage, the same applies. A spray on engine wiring may slow chewing on that one spot for a while, but the rats are still living nearby. Clearing the garage of food and nesting spots does more. See rats in your car engine.
What works instead
Cornell's IPM advice is prevention first: seal the home against entry and keep it free of spilled food and water. If rodents get in, remove access to food, water and shelter, then reduce the population by trapping or baiting. That plan has three parts:
- Remove food: pick up fallen fruit, store pet food and birdseed in sealed bins, and keep garbage lids closed.
- Trap: snap or enclosed traps along walls where you see droppings. See best rat and mouse traps.
- Seal: close every gap a mouse or rat can use with metal mesh, hardware cloth or sheet metal. See exclusion and sealing.
If you have already tried repellents and the noise is still there, a rodent inspection will show where they are getting in.
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(904) 593-1371Tap to callCommon questions
Do ultrasonic pest repellers work on mice?
Research hasn't shown it. Cornell NYS IPM says scientific evaluations found no effect on target pests.
Does peppermint oil keep rats away?
There is little evidence it gets rats out of a house. The smell fades quickly, and rodents get used to it.
Are mothballs safe to use for rats?
No. Mothballs are a pesticide for clothes moths in sealed containers, and using them elsewhere is off-label and a health concern.
What is the best way to keep rodents out?
Sealing entry points with metal-based materials and removing food sources, with trapping to remove rodents already inside.
Will a cat keep mice out of my house?
A cat may catch some mice, but it won't reach mice in walls or the attic and doesn't close the gaps they use.