A duct detector housing includes a housing cover and a housing body having a gas inlet and a gas outlet. The gas inlet is in fluid communication with a gas conveying duct. The housing body is adapted to have a detector therein and being complementary to the cover to form an interface therebetween. A binary mode securement mechanism for securing the cover to the housing body in either only an open or closed position is provided to overcome the uncertainty with conventional housings as to the integrity of the closure. A process for ensuring a cover is closed against a housing body of a duct detector housing includes placing the cover in complementary contact with a surface of the housing body and engaging the binary mode securement mechanism to provide only binary either positive or completely an open or closed position for the cover relative to the housing body.