ALL OBJECTS EMIT INFRARED (HEAT) ENERGY AS A FUNCTION OF THEIR TEMPERATURE. INFRARED ENERGY IS A FORM OF OPTICAL ENERGY AND IS REFLECTED BY MIRRORS AND REFRACTED BY LENSES. PIR DETECTORS USE OPTICAL COMPONENTS TO DETECT THE SMALL DIFFERENCE BETWEEN BACKGROUND INFRARED ENERGY IN A SPACE, AND ENERGY (BODY HEAT) EMITTED BY AN INTRUDER. THE ARTICLE FOCUSES ON FEATURES THAT DISTINGUISH THESE DEVICES FROM OTHER FORMS OF SPACE PROTECTION, SUCH AS IMMUNITY TO CERTAIN SOURCES OF FALSE ALARMS (E.G., MOVING OR VIBRATING SURFACES), ABILITY TO MONITOR PRECISELY DEFINED ZONES, AND MINIMAL POWER REQUIREMENTS. PARTICULAR ATTENTION IS DIRECTED TO THE BISPY PIR DEVICE, WHICH IS SAID TO ASSURE DETECTION WITHIN A SPECIFIED AREA, TO AVOID FALSE ALARMS, TO BE READILY UNDERSTOOD BY INSTALLERS, AND TO BE EASILY LOCATED AND CONTROLLED DURING INSTALLATION. THE COMPONENTS OF PIR DETECTORS, PRIMARILY THE BISPY, ARE EXPLAINED AND ILLUSTRATED IN DIAGRAMS. THE DEVELOPMENT AND MANUFACTURE OF PIR DETECTORS BY THE COMPANY THAT MARKETS BISPY ARE DESCRIBED. APPLICATIONS OF PIR DETECTORS TO PROVIDE EITHER WIDE-ANGLE COVERAGE OR SINGLE-ZONE, EXTENDED-RANGE COVERAGE ARE DISCUSSED, AS ARE FACTORS TO BE CONSIDERED IN INSTALLING PIR DETECTORS. (LKM)