peephole

thumb|View through a peephole thumb|Barack Obama looking through the [[Oval Office door peephole]] thumb|Door viewer in the gate of Vaxholm Fortress

A modern peephole, peekhole, spyhole, doorhole, magic eye, magic mirror or door viewer is a small, round opening through a door from which a viewer on the inside of a dwelling may "peek" to see directly outside the door. The lenses are made and arranged in such a way that viewing is only possible in one direction. The opening is typically no larger than the diameter of a button ().