The invention relates to a fire alarm call box for detecting gaseous and powdery combustion products, comprising at least one optical transmitter and at least two optical receivers, each for sending an electrical signal to an evaluation unit connected downstream. At least one of said optical receivers (28) is located beyond a direct range of radiation (8) of the optical transmitter (2) and acts as a scattered light receiver. At least one other optical receiver (4) is located within the direct range of radiation (8) of the optical transmitter (2). A gas sensitive layer (18) is connected upstream of this optical receiver (4). Upon contact with a specific gas, said layer preferably absorbs light components of a certain narrow wavelength range.