Quote from Niles in The Seal Who Came to Dinner
Niles: Let's get some lights on. [claps]
Frasier: Good Lord, what the hell is that?
Niles: Maris had it made after she lost power in a storm. Battery operated, works on a clapper so you can find it in the dark. Only problem was, the poor thing, try as she might, could never clap hard enough to activate it.