Abstract: A fire sensor device of the type capable of detecting flame and smoke. The fire sensor device has a detector unit having a condenser lens for determining variations in the brightness of a space on the basis of variations in the illumination thereof which occur due to the movement of flames of a fire or the presence of smoke therein. The fire sensor device has two frequency-detection circuits which have different set points and to which the detector unit is connected. The frequency and amplitude of a signal output from the detector unit and the number of pulses generated by the detector unit are computed, and the presence of a fire is detected on the basis of the duration of the signal.