Do those plug-in things to deter mice, actually work?

[Onlyconnect]

I have just bought one and am thinking about getting a couple more as I've just bought a house that has had mice in part of it. I'm hoping to stop them from coming in to start with.

They didn't work for us: we would watch the mice just saunter passed the plug-ins, seemingly unaffected. Had to go for the snap traps in the end.