A hazardous condition detection system for an enclosure, the system comprising: at least three detectors for detecting a hazardous condition, each of the at least three detectors mounted within the enclosure, each of the detectors configured to output a signal representing a first level of severity of the hazardous condition and a signal representing a second level of severity of the hazardous condition, the first level of severity less than the second level of severity, the first level of severity corresponding to a pre-alarm threshold and the second level of severity corresponding to an alarm threshold; and a controller coupled to receive the signals from each of the at least three detectors, the controller configured to: monitor an operational status of each of the at least three detectors; operate in a first mode when all of the at least three detectors are operational and, in the first mode, to generate an alarm signal when at least two of the at least three detectors output a signal at the alarm threshold level; and operate in a second mode when at least one of the at least three detectors is inoperative and at least two of the at least three detectors are operational and, in the second mode, to generate an alarm signal when one of the at least three detectors outputs a signal at the alarm threshold level and another of the at least three detectors outputs a signal at the pre-alarm threshold level. at least three detectors for detecting a hazardous condition, each of the at least three detectors mounted within the enclosure, each of the detectors configured to output a signal representing a first level of severity of the hazardous condition and a signal representing a second level of severity of the hazardous condition, the first level of severity less than the second level of severity, the first level of severity corresponding to a pre-alarm threshold and the second level of severity corresponding to an alarm threshold; and a controller coupled to receive the signals from each of the at least three detectors, the controller configured to: monitor an operational status of each of the at least three detectors; operate in a first mode when all of the at least three detectors are operational and, in the first mode, to generate an alarm signal when at least two of the at least three detectors output a signal at the alarm threshold level; and operate in a second mode when at least one of the at least three detectors is inoperative and at least two of the at least three detectors are operational and, in the second mode, to generate an alarm signal when one of the at least three detectors outputs a signal at the alarm threshold level and another of the at least three detectors outputs a signal at the pre-alarm threshold level. monitor an operational status of each of the at least three detectors; operate in a first mode when all of the at least three detectors are operational and, in the first mode, to generate an alarm signal when at least two of the at least three detectors output a signal at the alarm threshold level; and operate in a second mode when at least one of the at least three detectors is inoperative and at least two of the at least three detectors are operational and, in the second mode, to generate an alarm signal when one of the at least three detectors outputs a signal at the alarm threshold level and another of the at least three detectors outputs a signal at the pre-alarm threshold level.