The next time you are shopping at the local convenience store or renting a movie take a moment to tear your eyes from the shelves and glance around the store. You might notice a few strangely shaped mirrors hanging in the corners of the shop or placed at the head of each isle and wondered about their purpose. This security mirror is a special device designed to help the store owner prevent theft of their merchandise and other crimes that could jeopardize customer safety.
What makes a convex mirror so useful for the shopkeeper is its curved surface, which allows the viewer to see a much wider range of vision than a normal mirror would. Convex mirrors always reflect rays of light outwards, forming a smaller upright reflection called a “virtual image”. This effectively shrinks the image reflected into the mirror, allowing the viewer to see a much wider area than with a flat reflective surface. The curved surface of convex mirrors also enable the viewer to see around corners or down multiple branches of a hallway from one central viewpoint. When positioned at the intersection of several isles or in the corners of the room a convex security mirror will allow the shopkeeper to see down every isle in the store from one central location, forming a rudimentary panopticon that allows the store clerk to more effectively monitor the merchandise on each isle. This property is why people often place a safety mirror at blind intersections or at the entrance to a garage or alleyway to prevent accidents.
However, positioning the mirror is in itself a bit of an art form because you have to be sure to take the environment into consideration. Convex mirrors can see around corners, but they cannot see through walls. The mirror needs to be placed in a high location with a field of vision that is not obstructed by shelves or walls in order to be effective. The floor plan of the store and the mirror must work together to ensure that no spot is left unguarded. Convex security mirrors are also best used as theft prevention devices by allowing the shopkeeper to intervene during shoplifting or even deter a criminal from attempting the crime; however they cannot be used to identify a suspect or for any other purpose once the crime has been committed. For that reason convex mirrors are best used at part of a holistic security system that includes video monitoring and other safety measures.