This set of three mini sonic pest chasers uses varying volume & high frequency ultrasound to repel rodents from the home. Their small, discreet design is ideal for average size rooms. A blue LED light indicates when the unit is active. The sound produced cannot be heard by humans or non-rodent pets. Contains a piezo system with ceramic membrane, which creates louder sound & allows more controlled frequency. Plug them in today and protect your family and your property from unwanted rodent guests.