Do ultrasonic pest repellers work?

This is one of the highest-volume pest questions online, and the honest answer is short.

No. There is no reliable evidence that ultrasonic or electronic pest repellers control household pest populations, and the Federal Trade Commission has acted against manufacturers over exactly this claim.

What the FTC has actually done

In May 2001 the FTC’s Division of Enforcement sent warning letters to more than sixty manufacturers and retailers of ultrasonic pest-control devices, telling them that efficacy claims must be supported by competent and reliable scientific evidence and that unsupported claims may violate the FTC Act. Between 1985 and 1997 the Commission had already brought enforcement actions against six companies over false and unsubstantiated claims about ultrasonic devices for rodent and insect control, and it charged a further company in 2002.

This is unusual. Most product categories in this space have never attracted that level of regulatory attention, and the fact that this one has is itself informative.

Why they do not work

The physics is the problem. Ultrasound attenuates very quickly in air, does not pass through walls, and is blocked or absorbed by furniture, carpet, and soft furnishings — so the sound field inside a real room is nothing like the field a marketing diagram shows. Coverage claims quoted in square feet assume an empty box.

Beyond that, the pests are not distributed the way the device assumes. German cockroaches, bed bugs, and mice all spend most of their time inside harbourage — wall voids, cabinet gaps, mattress seams — where the sound does not reach at all. And where animals do perceive a novel stimulus, habituation is well documented: any avoidance response tends to fade within days as the animal learns the sound predicts nothing.

What the money is better spent on

A typical ultrasonic device costs about as much as a set of door sweeps and a tube of sealant, and the comparison is not close. A house mouse passes through a gap of about 6 mm. Sealing the gaps of that size or larger is unregulated, permanent, costs very little, and is the only measure that stops the problem recurring rather than repeating it.

• Exclusion — seal gaps of 6 mm or more with a material that cannot be gnawed through, fit door sweeps, and screen vents.
• Moisture correction — fix the leak, the drainage, or the condensation that made the space habitable.
• Sanitation — remove the food access, including pet food left out and grease films.
• Monitoring — place monitors to find out whether you have a population at all, and where it is.

Where the confusion comes from

Reviews for these devices are frequently positive, and that is worth explaining rather than dismissing. People buy them at the point when a problem is already peaking, which is often when it would have declined anyway — seasonal pest activity has strong peaks. Buyers also usually clean and tidy at the same time, which does real work. And an absence of sightings after installing a device is easy to attribute to the device rather than to the sanitation change that accompanied it.

None of that makes the buyers foolish. It makes the product’s evidence base indistinguishable from placebo, which is exactly what the FTC objected to.

Common mistakes

• Reading a coverage figure in square feet as if walls and furniture did not exist.
• Buying a device for bed bugs or cockroaches, whose populations live inside harbourage the sound never reaches.
• Treating a decline in sightings after installation as evidence, when a seasonal peak was already passing.
• Delaying exclusion work while waiting to see whether a device will work.