Peephole

For the System of a Down song, see System of a Down (album).

For the computer compiler techniques, see peephole optimization.

A visitor approaches a door, as viewed through the peephole

A peephole, peekhole, spyhole, doorhole or door viewer, is a small opening through a door allowing an individual to look from the inside to the outside.

In a door, usually for houses, mansions, castles, palaces, apartments, condominiumss, duplexes, townhouses or hotel rooms, a peephole allows the person behind the door the security of seeing outside without opening the door. Glass peepholes are often fitted with a fisheye lens to allow a wider field of view from the inside and little to no visibility from the outside.