Ultrasonic repellent is a device designed to deter pests, such as mosquitoes and rodents, using high-frequency sound waves. These sound waves are typically above the range of human hearing, making them inaudible to people but irritating to certain animals. The idea is that the unpleasant sound will encourage pests to leave the area. These devices are often marketed as a safe and eco-friendly alternative to chemical repellents. They can be used indoors or outdoors and are usually powered by batteries or electricity. However, the effectiveness of ultrasonic repellents can vary, and scientific studies have produced mixed results regarding their ability to repel pests.