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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 ().
In a Peephole Is One Way Viewer
''Popular Science'', July 1950, p. 153, right-side.
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 ().
In a door
A door is a hinged or otherwise movable barrier that allows ingress (entry) into and egress (exit) from an enclosure. The created opening in the wall is a ''doorway'' or ''portal''. A door's essential and primary purpose is to provide security b ...
, usually for apartment
An apartment (American English), or flat (British English, Indian English, South African English), is a self-contained housing unit (a type of residential real estate) that occupies part of a building, generally on a single story. There are ma ...
s 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
A fisheye lens is an ultra wide-angle lens that produces strong visual distortion intended to create a wide panoramic or hemispherical image. Fisheye lenses achieve extremely wide angles of view, well beyond any rectilinear lens. Instead of pr ...
to allow a wider field of view
The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.
Humans a ...
from the inside.''Popular Science'', July 1950, p. 153, right-side.
Preventing inside viewability
Simple peepholes may allow people outside to see inside. A fisheye lens offers little visibility from the outside, but that can be defeated using a peephole reverser. Some peepholes have a shutter that falls down on the hole when nobody inside is holding it. Digital peepholes have a camera outside and an LCD screen inside, without any information going from the inside to the outside. Another design to prevent people outside from seeing in involves the outside-facing lens projecting an image onto a semi-opaquefrosted
Frosted (stylised as FroSTed) was an American pop punk band, founded by ex-Go-Go's guitarist and singer Jane Wiedlin in 1995. The band was so-named because ''"it sounds sweet"''.''The Daily Aztec''link) The letters S and T were capitalised in tr ...
or ground glass screen. An inside viewer can see the other side of the door from an arm's length away, rather than by peering a small hole, while the frosted glass finish makes it impossible for someone to look through from the outside. There are drawbacks to the projection method: the area to be viewed must be well lit, and installation requires a much larger hole in the door than a traditional peephole.
References
{{commons category, Peepholes Door furniture Security technology