The Black & Decker Pest Repeller is supposed to repel pests of all kind, from rodents to roaches, by emitting an ultra-sonic sound. Each repeller is slightly larger than the palm of an average person's hand and plugs directly into an electrical outlet. The repeller is chemical-free and safe for the environment. The ultra-sonic sound does not disturb cats or dogs or small children. The problem, though, is that the sound does not seem to disturb pests either.
I purchased a three-pack of the Black & Decker Pest Repellers in order to keep cockroaches away. The repellers have had no discernible effect on the roach population in my home, and I have actually caught cockroaches hiding behind the repellers.
I do not have mice, spiders or other vermin in my home. It is entirely possible that the repellers are very effective against these other types of pests. However, they seem to be completely ineffective against cockroaches. If you have a roach infestation, save the $16.99 you'd pay for a three-pack of repllers and invest instead in some heavy duty pesticide. Bug spray may be toxic and it may smell awful, but at least it works.