There is described a duct detector (1) and components (2, 3, 6) for duct detectors. In one form the duct detector (1) includes: a port unit (3) and detector unit (2). The port unit (3) is mountable to a duct in use so as to position one or more ports in the duct. The detector unit (2) includes a detection region. The port unit (3) and detector unit (2) are reconfigurable between a close coupled configuration and a separated configuration in which the units (2,3) are mountable with a variable separation between them and coupled by one or more elongate conduits (12A, 12B) to provide fluid communication between the units (2,3).