Does ultrasonic pest control work?

What the FTC has done

In May 2001 the FTC sent warning letters to more than sixty manufacturers and retailers of ultrasonic pest-control devices, stating that efficacy claims must be backed by competent and reliable scientific evidence and that unsupported claims may violate the FTC Act. Between 1985 and 1997 it had already brought enforcement actions against six companies over ultrasonic device claims, and charged another in 2002.

Very few product categories in this field have drawn that level of regulatory attention. That this one has is itself informative.

Why the physics does not work

Ultrasound attenuates rapidly in air, does not pass through walls, and is absorbed by furniture, carpet, and soft furnishings. The sound field in a furnished room is nothing like the diagram on the box, and coverage figures quoted in square feet assume an empty space.

The pests are also in the wrong place. German cockroaches, bed bugs, and mice spend most of their time inside harbourage — wall voids, cabinet gaps, mattress seams — where the sound does not reach at all.

Where an animal does perceive a novel stimulus, habituation is well documented. Any avoidance tends to fade within days once the sound predicts nothing.

Why the reviews are positive anyway

This is worth explaining rather than dismissing. People buy these devices when a problem is already peaking, which is often just before it would decline anyway — seasonal activity has strong peaks. Buyers usually clean and tidy at the same time, which does real work. And an absence of sightings afterwards is easy to credit to the device rather than to the sanitation change.

Common mistakes

• Reading a square-footage coverage claim as though walls and furniture were not there.
• Buying one for bed bugs or cockroaches, whose populations sit inside harbourage.
• Crediting a seasonal decline to the device.
• Postponing exclusion work while waiting to see whether it works.