The Kidde i12060 is a compact, round unit, about 6 inches in diameter, about 2 inches thick and weighing around 10 ounces. This unit needs wiring to an electricity supply and is fixed to the ceiling using an adjustable mounting unit. It uses a back-up battery which loads onto the front of the device to make installation quicker and easier as the unit doesn’t need to be removed from the ceiling at all.