Less than two inches deep, SuperDuct four-wire smoke detectors are suitable for installation in ductwork, where space is limited. SuperDuct detectors feature removable dust filters, conformally coated circuit boards, and optional water-resistant gaskets to keep contaminants away from components. They include industry standard sampling tube mounting holes to simplify retrofit applications. SuperDuct detectors use differential sensing to prevent gradual environmental changes from triggering false alarms. A rapid change in environmental conditions, such as smoke from a fire, causes the detector to automatically signal an alarm condition but dust and debris accumulated over time does not change alarm sensitivity. The relay output may be configured for operation independent of the duct detector. A dedicated dirty/trouble LED on each unit offers immediate at-a-glance information even when the cover is closed. The controller can be installed up to 15 feet from detector and one controller can support up to two detectors. Up to 15 controllers can be interconnected for multiple fan shutdown. Remote Test/Reset stations are available to provide alarm testing and indication from a remote location. Two-wire SuperDuct detectors are also compatible with 5956A remote alarm LEDs.