Surveillance equipment allows for the continous monitoring of people and places, the desire for which has existed forever. In some cases, the observer wishes to be hidden from the people being watched or listened to; examples include hidden cameras and "bugs," or hidden listening devices. Other times, surveillance equipment is made as visible as possible through signs, conspicuous camera and monitor placement, and other means. In all cases, however, surveillance equipment enhances the observers natural ability to see and listen.

Strategic locations, either man-made or natural, were early forms of visual, or optical, surveillance equipment. A castle tower, the crow's nest of a ship, or a tall tree all provided the "bird's-eye view" essential for surveillance. Combined with optical inventions such as the telescope, early surveillance relied primarily on the human eye.

Modern visual surveillance equipment began with the development of photography. During the American Civil...