This is a harmonized UL and ULC binational Standard for Smoke Detectors for Fire Alarm Systems. This Standard sets forth requirements for smoke dectectors and accessories, including mechanical guards to be employed in ordinary indoor locations in accordance with the following: In the United States: NFPA 72, National Fire Alarm and Signaling Code In Canada: CAN/ULC-S524, Standard for Installation of Fire Alarm Systems; National Building Code of Canada; and National Fire Code of Canada.