Research has found that these ultrasonic cure-alls are not effective repelling bats from your home and yard.
The Myth of Ultrasonic Repellent
Ultrasonic pest repellent is based on the idea that high-frequency sounds can be such a nuisance that pests such as bats will be repelled. It's not unlike how dogs will bark at the sound of a dog whistle. The sounds emanating from these machines cannot be heard by humans, but supposedly can be heard by everything from bats to fleas and ticks.
According to the U.S. Department of Agriculture, most pests hear in the same range as humans do. Some claim that a bats hearing is supersensitive because of its use of sonar in hunting, but there have been no findings that these ultrasonic machines cause problems or are a nuisance to bats.
Bats are also flying animals, and scientists have shown that these ultrasonic sounds are at half strength at 15 feet and completely gone at 30 feet. There have been some successes in using high-frequency sounds in deterring bats, but nothing from low-cost commercial products. In fact, if the rats and bats were repelled by the devices, your dogs, cats and other pests would be also.
Effective Ways to Eliminate Bats
There are other ways to eliminate bats from the home that have been proven. According to the U.S. Geological Survey, Naphthalene is the only chemical approved by the Environmental Protection Agency in the elimination of bat infestation. While the strong odor of Naphthalene will deter bats, it can also be harmful to humans if inhaled.
Bats are nocturnal animals and there has been success in repelling bats using artificial lights. Bats will flee an area that is constantly lighted or retreat to the periphery. Also, the sounds of bats in distress have also been shown to repel bats, as well as the use of sticky traps like those used against mice and rats. This is not the most humane way to eliminate your bat problem and would require you to retrieve and dispose of the bats.