Introduction The purpose of this guide is to provide information concerning the proper application of smoke detectors used in conjunction with Fire Alarm Systems. It outlines basic principles@ which should be considered in the application of early warning fire and smoke detection devices. Operating characteristics of detectors and environmental factors@ which may either aid@ delay or prevent their operation are presented. Fire protection engineers@ mechanical and electrical engineers@ fire service personnel@ fire alarm designers and installers will find the contents both educational and informative. Though this information is based upon industry expertise and many years of experience@ it is intended to be used only as a technical guide. The requirements of applicable codes and standards@ as well as directives of the Authorities Having Jurisdiction (AHJ's) should be followed. In particular@ NFPA 72 for installation of detectors and for testing of systems are key elements in the effectiveness of smoke detection systems.