The big cheese mouse and rat repeller 3 pack uses ultrasonic sound waves to create a distressing noise audible to rodents only the nature of sound waves mean that any obstruction creates a barrier and the waves cannot go any further mice tend to venture back into areas where they may find food to avoid this best practise before using the repeller is to thoroughly clean the area and remove all possible food sourcesthe repellers are a deterrent only and so vermin may venture back occasionally