We used to get field mice out in the country up in ME and tried everything under the sun before we finally put out poison, which worked well for us.
Down here in VA, though, we don't have a mouse problem, we have a squirrel problem. We bought those plug-in things you asked about AND we bought some sprinkles that we spread around where they were hiding (our attic) to repel them (they hate the taste and smell, but it isn't poison). Once my husband hit a couple of them with his paintball gun (it doesn't kill them), he spread the sprinkles and plugged in the thingies and we haven't had not ONE squirrel in the whole month since! It has been awesome!
The best news is that the plug-in thingies are in the attic, but don't bother our dog and cat in our bedroom below - I was really worried about that.
If all else fails - get an exterminator. It also helps to find where they are coming in and block it off.
at 5:26 PM on Apr. 22, 2009