spyholes

A spyhole, also known as a peephole or a door viewer, is a small optical device installed in a door or wall that allows someone on the inside to see out. Typically, spyholes consist of a convex lens that provides a wide-angle view of the area outside, making it easier to identify visitors without opening the door. The lens is usually housed in a metal casing and can be fitted into doors of varying thickness.

The primary purpose of a spyhole is to enhance security and privacy. It allows residents to verify the identity of callers before deciding whether to grant them entry, which can deter unwanted visitors, salespeople, or potential intruders. In residential settings, spyholes are common on front doors and apartment doors. They are also found in hotel rooms, office doors, and other locations where controlled access is desired.

The design of a spyhole involves a specific optical principle. The wide-angle lens creates a panoramic view, but it also distorts the image, making objects appear smaller and farther away than they actually are. This distortion is a trade-off for the increased field of vision. Some modern spyholes incorporate digital technology, featuring small cameras and screens that offer a clearer, more detailed image and can even record short video clips. These digital peepholes can also include features like motion detection and two-way audio communication.