Abstract: A housing for a fire detector has a circumferential area including a series of vanes or slats, each positioned at an angle with respect to the tangent at the periphery of the housing. The angle is about 45.degree., which not only allows ready entrance of gases through the major portion of the "window" defined by the vanes, but also prevents particles from passing straight through the housing and out the other side. This effects good mixing of the gases, better detection of combustion particles, and also decreases the likelihood of spurious or incorrect signals due to extraneous air currents.