Peephole

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

A 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 dime (0.7 inches, 18 mm).

In a door, usually for apartments or hotel rooms, a peephole enables to see outside without opening the door nor revealing one's presence. Glass peepholes are often fitted with a fisheye lens to allow a wider field of view from the inside.[1]

  1. ^ Peephole Is One Way Viewer, Popular Science, July 1950, p. 153, right-side.