D4120 Duct Smoke DetectorThe Notifier InnovairFlex D4120 and D4120W multi voltage 4 wire photoelectric duct smoke detectors features a pivoting housing that fits various applications: both square and rectangular footprints and mounts to round or rectangular duct work. The multi voltage 4 wire design allows the D4120 and D4120W duct detectors to be used as a 4 wire device on a conventional fire detection system or as a stand alone part of a HVAC system. These units sense smoke