Ultrasonic pest repellers are devices designed to deter pests like rodents and insects using high-frequency sound waves. These sound waves are typically above the range of human hearing but can be disruptive to pests, encouraging them to leave the area. The technology is often marketed as a humane and chemical-free alternative to traditional pest control methods. These devices are easy to use; simply plug them into an electrical outlet, and they start emitting sound waves. While some users report success, scientific studies on their effectiveness are mixed, and results can vary based on the type of pest and the environment.