Ultrasonic and electronic pest repellers

The claim

A plug-in or battery device emits ultrasound that drives away insects, rodents or both.

What the evidence actually shows

This is one of the few garden and household claims where the literature is not merely thin but decisively negative.

A Cochrane systematic review of electronic mosquito repellents for preventing bites and malaria found no randomised controlled trials existed, and that all ten field studies showed no difference in the number of mosquitoes caught on bare body parts with or without a device running. The review concludes there is no evidence to support their promotion or use - unusually direct language for Cochrane.

For insects generally, a study in the Journal of Economic Entomology tested four commercially available ultrasonic devices against bed bugs in two-choice arenas. Female bed bugs were equally likely to occupy the arena with sound as the one without. The devices neither repelled nor attracted them.

Why the category survives

Because the mechanism sounds plausible, the output is inaudible so there is nothing to contradict, and any absence of pests is attributed to the device. It is a claim structured so as to be unfalsifiable by the user.

What to do instead

Physical exclusion, habitat management and, where needed, an appropriate registered product. For mosquitoes specifically, eliminating standing water and using evidenced repellents on skin or clothing.