From a review at Amazon
An amazon review of another model said several members of her family got headaches with it.
We put 10 of these in our cabin and I got a headache in 24 hours .
From (118) Proof That Ultrasonic Pest Repellers Are A Scam: Class Action Lawsuit For Fraud. Mousetrap Monday. - YouTube, which tested another brand.
They also say the Bell + Howell has the most misleading advertising and has had a class action law suit filed against it.
4 Types of Insect Repellent to Skip - Consumer Reports
The FTC has investigated several sonic repellent makers for false advertising.
5 Best Ultrasonic Pest Repellers - Mar. 2021 - BestReviews
It’s important to note that this type of device is not effective against all pests. Certain insects, like ants, are more resilient than others when it comes to ultrasonic frequencies. Some studies have also shown that ultrasonic repellers may even attract critters (such as mosquitos) into your dwelling. Correct positioning and use of these units is the best way to maximize effectiveness, but don’t think of it as an instant solution to pest problems. It takes time for repellers of this type to produce a measurable effect.
Do Ultrasonic Pest Repellers Really Work? | Terminix
While some ultrasonic repellents may have a minor short-term impact on some pests, the research is nearly universal: Ultrasonic pest repellers are not an effective
Ultrasonic Pest Repellers: Solution or Scam? - InterNACHI®
One extensive test performed by Kansas State University in 2002 found that the devices were effective at repelling some insects, such as crickets, but the same devices had little effect on cockroaches. Ants and spiders were unaffected by any of the devices.
Even models proven successful in tests are unlikely to perform adequately in real-world situations, where signal strength rapidly diminishes.
Safety concerns have arisen, too; some users have reported that the sound can weaken the clarity of telephone conversations, interfere with burglar alarm systems, and cause muting in hearing aids.
InterNACHI® is the world’s leading association for home inspectors. We provide free training, online testing and certification.
PubMed Central, Proc Math Phys Eng Sci. 2016 Jan; | ncbi/nih.gov This paper presents new measurements that demonstrate human exposure to airborne ultrasound in public places, including railway stations, museums, libraries, schools and sports stadia. It argues that the guidelines for protecting humans from airborne ultrasound vary and are uniformly inadequate: for energy above 22.4 kHz, they are based on avoiding ultrasonically induced hearing damage at the lower frequencies used to understand speech, taking no account of reports of the ability of airborne ultrasound in occupational settings to cause nausea, dizziness, tinnitus, fatigue, migraine and headaches. Research has shown that airborne ultrasound has the potential to cause nausea, fatigue, and headaches ,,,,,’ .
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