I've bought two more of these. I've got my kitchen back at last. Mice had turned our kitchen into the last place you'd want to prepare food! I had to warn visitors before they went in there. Even blocking holes, sealing the skirting boards, using traps etc hadn't worked-they soon avoided them. All food was in new storage boxes or high cupboards. This cut down the droppings etc but you'd still see a mouse every evening and hear them at night-it's really horrible as other 'sufferers' will know!
The first evening we used this my friend saw a mouse acting 'strangely', it was running around at the far end of the kitchen. Within two to three weeks we had no mice at all and there was an immediate reduction in activity before that-just a few droppings. I'd heard that they drink water from backs of fridges etc and these droppings were the last to go completely.
They only work within the room they're in so I've got some for the ceiling space and another room. I don't know if it's connected but there is less noise in the walls etc though this device doesn't directly influence that.
If you have the same problem I'd advise you to seal all holes, put all food out of reach or in plastic boxes and keep everything clean of crumbs, grease etc. Try simple, wooden (or humane)traps first but if that doesn't work I'd recommend these for a room. I'm very, very happy with it and keep it in the kitchen just to be on the safe side. Good luck to anyone else with this problem.