An electrical device that contains a reservoir of a liquid specially manufactured for the purpose of producing a smoke effect. Useful for simulating smoke, mist, fog (it's also called a fog machine), and simply producing a thin layer of slightly opaque atmosphere to reveal the beams of light. There are various ways to control the smoke, including the use of a dry ice "locker" that will cool the stream of smoke and make it "lay down" on the stage floor for those misty moor looks.