2023 UPDATE TECHNOLOGY: The dual ultrasonic and electromagnetic chips of our ultra sonic pest repellers emit frequencies ultrasonic interfering the auditory and nerve system of the pest, making them feel uneasy and uncomfortable so that pests, mice, rodents and mosquitoes away from your home. EASY TO USE: Just plug the ultrasonic pest repellers into the socket. If the pest repellent displays a blue light and flashes, it means the best ultrasonic pest repeller is working normally. No battery required, just plug repellers and play. Please make sure to install it vertically 10-50 inch away from the floor. And make sure there are no barriers like curtains or cabinets covering in front of the ultrasonic pest repeller. SAFE FOR HUMAN \u0026 PETS: The ultrasonic frequency of the electronic mosquito repellent is inaudible to humans and pets, environmental-friendly,The rodent repellent ultrasonic plug-in does not eliminate insects, but removes them from the covered area without using chemicals