An ultrasonic pest repeller is a device designed to deter pests like rodents and insects using high-frequency sound waves. These sound waves are typically above the range of human hearing, making them inaudible to people but uncomfortable for pests. The idea is that the unpleasant sound will encourage pests to leave the area. These devices are often marketed as a humane alternative to traditional pest control methods, such as traps or poisons. They are easy to use, simply requiring a power source to operate. However, the effectiveness of ultrasonic pest repellers can vary, and they may not work for all types of pests.