Mosquito repellent (pack of 4) Ultrasonic Repellent - This is our advanced version. Using ultrasound theory, change frequency to stimulate the auditory system of mosquito and other pests, make them unbearable and feel uncomfortable. Wide Coverage Area - Each ultrasonic electronic pest repellent is effective for a large area up to 800-1300ft. Please note that ultrasonic waves cannot pass through walls. Although our pest repellent works well, if you have a large infestation we recommend placing our insect repellent in every room. Environmentally and Safety Friendly - The product is non-toxic and environmentally friendly. environment, our repeller is 100% safe and effective, the ultrasonic frequency emitted by this machine is inaudible to humans and pets. Safe for kids, family and pets. However, if you have a hamster pet at home, do not use this ultrasonic repeller. Easy to use - This machine should be installed 80-120 centimeters from the ground. And vertical to the floor and plug into the power outlet. It can be plugged directly into the AC 110V power outlet (power range: AC 90V-250V Frequency: 50-60HZ). Commonly used in homes, warehouses, stores, hotels, hospitals, offices, etc. Large areas may require more than one unit.