The Hochiki DH-99 Addressable Duct Smoke Detector pro-vides early detections of smoke and products of combustions present in the air, moving through the HVAC ducts in Commercial, Industrial, and Residential applications. The DH-99 is designed to prevent the recirculation of smoke in areas by the Air Handling Systems, fans and blowers. Complete systems may be shut down in the event of smoke detection. The DH-99-A operates on the Digital Communication Protocol (DCP).