The Edwards EST SIGA-SD is a Signature Series intelligent duct smoke detector designed to provide early smoke detection within HVAC ductwork. It incorporates a Signature Series photoelectric sensor using light-scattering technology and processes analog data through an onboard microprocessor to make alarm decisions based on digital filtering and historical pattern analysis. The detector continuously samples air through a field-installed sampling tube (ordered separately) and exhaust tube (included), detecting smoke based on percent obscuration levels. It includes a built-in Form C auxiliary alarm relay for controlling HVAC shutdown or other ancillary equipment. The SIGA-SD supports electronic addressing via the Signature Loop Controller, offers environmental compensation with differential sensing, and provides dirty or defective sensor diagnostics. It is UL and ULC listed for duct smoke detection applications.