PestChaser Sonic Technology PC3000 Direct Plug-In Electronic Rodent Repellers, Set of 3 Plug into wall socket, emit high-frequency sound to repel rodents Sound inaudible to humans and non-rodent household pets Three units, each 3-1/8 inches square Function for 5-7 years or more 90-day full-refund satisfaction guarantee; 3-year warranty against defects