A combination airborne substance detection apparatus includes an enclosure, a first module disposed within the enclosure for detecting the presence of a quantity of a first airborne substance, a second module disposed within the enclosure for detecting the presence of a quantity of a second airborne substance, and an alarm module for producing a first perceivable emission when the first substance is detected and for producing a second perceivable emission when the second substance is detected. The first perceivable emission includes at least one of an audible and a visible emission that is distinguishable from the second perceivable emission. The first and second detector modules are each capable of independently and continuously detecting the first and second substances, respectively.