The Air Products & Controls SM-501 Series Duct Smoke Detectors provide early smoke detection and sense combustion products present in air moving through HVAC ducts. The smoke detectors sample air using intake sampling tubes, which are sold separately. A standard length exhaust tube is provided with each detector. The SM-501 Series is designed to operate in duct widths from 6 in. (15 cm) to 10.0 ft. (3.05m) with an air velocity from 500-4000 fpm (2.5-20.3 mps). Complete systems may be shut down in the event of smoke detection. These detectors are proven performers in Building Automation Systems, BAS.