We get asked this on most inspections, usually because there is already a plug-in device in the hallway. The honest answer is that they do not reliably work, and the reasons are physical rather than a matter of brand quality.
What the evidence shows
Ultrasonic pest repellers have been studied repeatedly. The consistent pattern is that rodents may show an initial avoidance response, and that the response fades — often within days.
Regulatory attention in the US has focused on unsupported efficacy claims by manufacturers of this category of device. That is the clearest signal available: the marketing has repeatedly outrun the evidence.
Why the physics works against them
Ultrasound does not pass through solids. High-frequency sound is blocked by walls, doors and furniture. A device in a hallway does nothing inside a wall void, above a ceiling, in an attic or under a kitchen cabinet — which is precisely where rodents are.
It attenuates fast. High frequencies lose energy over distance far more quickly than low ones. Effective range in a real room is short, and manufacturer coverage figures assume an empty box, not a furnished house.
Shadowing. Any solid object creates an acoustic shadow behind it. A cluttered garage or a joisted attic is nearly all shadow.
Habituation. This is the decisive one. Rodents adapt to persistent non-threatening stimuli. A sound that never precedes anything harmful stops registering as a threat. Once the food, warmth and shelter are on the other side of it, motivation beats mild annoyance.
The Tucson-specific problem
Attics and engine bays are the two places rodents cause the most expensive damage here, and both are close to worst-case environments for ultrasound. An attic is a maze of joists, ducts and insulation — insulation in particular absorbs high frequencies extremely well. An engine bay is a dense metal enclosure that blocks and reflects the signal chaotically.
What about the pets question
Dogs, cats, rabbits, ferrets and rodent pets all hear well into ultrasonic ranges. Most tolerate these devices, but some animals are visibly stressed by them. If you keep pet rodents, be aware you may be running a stress device in their room. Reported effects on hearing aids and some electronics are also occasionally raised.
Where the money should go instead
Roughly in order of return:
- Exclusion. Sealing entry points is the only measure that produces a permanent result. Everything else manages symptoms.
- Habitat removal. Woodpiles, yard clutter, fallen citrus, dense planting against walls. Free, and it addresses cause.
- Canopy clearance. Cutting the tree-to-roof bridge removes the primary roof rat route.
- Proper trapping. Correct type, correct placement, sufficient quantity, checked daily.
- A light in the engine bay. Cheap and genuinely effective against pack rats.
Other products worth a straight answer
Peppermint oil. Mild, brief deterrent effect at high concentration. Evaporates. Does not move an established population.
Mothballs. Ineffective at the quantities people use, and using them outside their labelled purpose is a misuse of a pesticide. The vapour is not something to have in living space.
Dryer sheets. No meaningful effect. Rodents have been found nesting in them.
Predator urine granules. Some short-term effect outdoors. Degrades quickly in sun and rain.
If you already own one
There is no need to throw it out — it is not doing harm in most households. Just do not count it as part of your plan. If you have a device running and you are still hearing activity, that is the device answering the question for you.
Not sure what you are dealing with?
A free inspection identifies the species, every entry point and the scope of work — in writing, before anyone quotes you a number.
