Peepholes

A peephole, also known as a door viewer or spy hole, is a small optical device embedded in a door that allows a person inside to observe someone outside without opening the door. It is commonly used to verify visitors and enhance security in homes, apartments, and some commercial buildings.

Most traditional peepholes are optical devices that use two lenses to create a wide field of view. The outer lens projects the scene inside through a small hole to an inner eyepiece, producing a view that is often wider than what the eye could see at the same distance. Field of view depends on design and can be very wide in high-end models.

Modern options include digital door viewers, which place a small camera on the outside of the door and a display screen inside. These devices often include night illumination, digital zoom, and the ability to capture or store images. Some models are reversible for doors of different thicknesses or for left- and right-handed installation.

Installation usually requires drilling a hole through the door and attaching a housing that holds both lenses or a camera and screen. The process varies by model and door thickness; installers should follow manufacturer instructions and ensure proper alignment, weather sealing, and security against tampering.

Limitations include potential image distortion at certain angles, reduced effectiveness on very thick or solid doors, and the risk that a cheap unit may be bypassed or damaged. Peepholes do not replace other security measures, and alternative devices such as doorbells with cameras are available for enhanced monitoring.