My father in law bought the Maier Pest & Mosquito Repeller in China. It is a high powered ultrasonic repeller that has a soft glow night light. We plug it in a socket 24 hours a day. It is supposed to cover an area of up to 1, 600 sq. ft or 150 sq. m. The product manual however does not include if the area is covered with walls.
Anyway, what we have noticed now is that the mice are no longer seen running around the floors. And the cockroaches are no longer flying around the living, although they are still in the kitchen. I can't say the same about mosquitoes though, because I still get bitten even if my computer is just near the repeller.
The problem with this product, however, is that it shoes pests from your house to the neighbors' houses. They do not really exterminate the pests, so while we are enjoying a pest free home, our neighbors are probably suffering from pests.
Problem alsom the product comes from China, so there is definitely no warranty.