Abstract: The smoke detector contains an optical measuring chamber, having a sensor arrangement (2) with at least one light source (12, 12?) and one light receiver (11), and a labyrinth system (7) with screens (16) arranged on the periphery of the measuring chamber. The light source (12, 12?) and the light receiver (11) are each arranged in a housing (14, 15; 13). The above-mentioned housings (14, 15; 13) have an elongated shape and a small window opening The at least one light source (12, 12?) and light receiver (12, 12?) are arranged in the rear part of their housings (14, 15; 13), so that between the window openings of the housings (14, 15; 13) and the light-penetrated optical surfaces of the at least one light source (12, 12?) and/or the lens of the light receiver (11) a relatively large gap is formed. This gap is preferably greater than the diameter of the above-mentioned optical surfaces, or of the above-mentioned lens.