Victor, 2 Pack, Mini, Plug, Pest Chaser, Varying Volume & High Frequency Ultrasound Repels Rodents, Small, Discreet Design Ideal For Average Size Rooms, Blue LED Light Shows Unit Is Active, Cannot Be Heard By Humans Or Non-Rodent Pets, Contains Piezo System With Ceramic Membrane, Creates Louder Sound & Allows More Controlled Frequency.