Repellents, traps and other tools meant to eliminate or prevent pest attacks or invasions can sometimes have questionable health effects or be considered inhumane. Ultrasonic devices are meant to repel pests through a high-frequency sound that humans cannot hear. An examination of the scientific trial history of ultrasonic repellents can determine whether they really work.
The history of scientific trials performed on ultrasonic pest control devices is, unfortunately, short and uneventful. Some say that because of such a serious lack of evidence involving the effectiveness of such devices, they most likely are ineffective. Others argue, however, that simply because there isn't an abundance of proof to the contrary doesn't mean ultrasonic repellents don't work.
The Clinician's Guide to Mosquitoes and Mosquito Repellents, a collection of information gathered from peer-reviewed research studies and published by the Annals of Internal Medicine, concluded that "Ultrasonic devices, outdoor bug 'zappers,' and bat houses are not effective against mosquitoes." A blinded, controlled trial reported in May 2000 found similar results. It said in its summary, "The ultrasound device used was not effective against mosquitoes in this strictly controlled trial."
A study performed in the Philippines set out to test three different ultrasonic devices that each emitted sounds of different frequencies against rats. Although a small level of effectiveness was observed, the results were "highly dependent upon ultrasonic frequency, intensity and the pre-existing rodent-infestation condition" according to the abstract of the study's report. While higher frequencies may provide some protection against rats, there are so many factors involved that ultrasonic devices may not necessarily be a cure-all for rodent infestations.
Based on the limited amount of proof available, the efficiency claims of ultrasonic repellents are highly suspect. Many claim to have seen results from such devices, however, so ultimately the decision is up to the consumer whether or not to invest money in such electronics. If ultrasonic repellent is something you'd still like to try, then do so. Scientific tests can only show relationships between two variables and occasionally do not hold up in all circumstances. However, given the results shown above, purchasing a device at a location that accepts returns is the best recommendation.