Abstract: In a condition detector for detecting conditions in more than a single region, a pilot flame is established by a controlled supply of fuel to a burner at the bottom of a vertically elongate chimney. The chimney is closed at the bottom and combustion air for the flame enters the top of the chimney and flows downwardly therein. The flame is extinguished, or diminished, when combustion products or gases other than oxygen enter the upper end of the chimney and reduce the supply of oxygen to the flame. A flame detecting switch device adjacent the pilot flame burner, is actuated in response to extinguishing, or diminishing of the flame and may be connected to cause a signal, such as an alarm, to be actuated. The detector is mounted in an enclosure and ducts lead from the enclosure to regions which are to be monitored by the detector whereby the gases from the regions influence the detector.