https://www.bbc.com/news/magazine-20669080

A 2010 review article examined 10 field studies, in which ultrasonic repellent devices had been put to the test, and concluded that they "have no effect on preventing mosquito bites" and "should not be recommended or used"

https://www.consumerreports.org/insect-repellent/five-insect-repellent-products-to-avoid/

https://www.consumerreports.org/cro/insect-repellent/buying-guide/index.htm

Sonic Repellents

Ultrasonic devices claim to emit high-frequency sounds that are too high for humans to hear but are just the right frequency to drive pests, including mosquitoes, away. The trouble is, there's no proof that they work.
The Federal Trade Commission has investigated several sonic repellent makers for false advertising. In 2016, the New York Attorney General's Office sent cease and desist letters to the makers of two specific brands of sonic repellent—STAR Ultrasonic Pest Repeller and iGear iGuard 2.0 Ultrasonic Insect Pest Repeller. "Numerous scientific studies show that [these devices] don't repel mosquitoes and may even attract mosquitoes," the attorney general said.

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https://kremmania.hu/kremek/off-protection-plus-pumpas-szunyogriaszto

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