Imperial Doorbells are mechanically operated, requiring no batteries wiring or electricity. The doorbell simply fits onto the inside of your front door and gives maintenance free, reliable service. The doorbell uses a clockwork action, and needs only an occasional winding of the dome and they give a loud ring, using the door itself as a sounding board. They will continue to ring as long as the bell push button is pressed and visitors can clearly hear that your doorbell is in working order. The clockwork mechanism is released by a thin rod that passes through the door to a bell push button on the outside. This rod is adjustable for different door thicknesses, but where doors are particularly thick, we can supply longer rods. The bell units measure 78mm, (3") in diameter, when fully wound, the bell will ring for approximately 75 seconds, and since a typical visitor will press the bell push for between 2 and 3 seconds, the mechanism will support up to 30 rings. The standard doorbell kits come with the bell pushes shown in the kit images, however, there are additional bell push options to suit different door furniture and tastes.