Rats and mice pose serious health risks, but traps and poisons come with a heavy price. Poisons can endanger children and pets while inhumane traps require the handling of potentially disease-bearing rodents. Neither poisons nor traps provide long-term protection since more rodents will likely replace the ones you've killed. It can be an unending cycle. The PestChaser Electronic Rodent Repeller puts the emphasis on non-toxic prevention, instead of after-the-fact toxic intervention. The PestChaser emits high frequency ultrasound waves between 32 and 62 kHz to create an acoustically hostile environment that repels rodents from sound-protected areas, over the long term. It's kinder than traps, safer than poisons, and inaudible to people and non-rodent pets. New handy 4-pack provides coverage for 4 rooms (i.e. kitchen, living & family room and garage or basement) each up to approx. 800 square feet. The Direct Plug-In fits discreetly into any unobstructed wall outlet and works best in rooms where there is a visible electrical outlet unobstructed by furniture, drapery, or other objects. Not recommended for use with an extension cord.