PRODUCT APPLICATION The SM-501 Series Duct Smoke Detector provides early detection of smoke and products of combustion present in air moving through HVAC ducts in Commercial, Industrial, and Residential applications. The unit is designed to prevent the re-circulation or spread of smoke by air handling systems, fans, and blowers. Complete systems may be shut down in the event of smoke detection. The SM-501 model will operate on any one of four input voltages (230VAC, 115VAC, 24VAC, or 24VDC). The SM-501 allows up to 30 detectors to be interconnected for many common functions.