A method for reducing false detects may include emitting an infrared light beam from a primary emitter to a primary monitor detector, measuring a first voltage value using a primary receive detector and setting a primary smoke alarm flag corresponding to a primary channel if the first voltage value is above a first threshold value. A load detector 28 for detecting stock level is provided on inlet part 16a of the tube type supplying unit 16, a detection rod 29 for detecting the level is suspended in the tube type supplying unit 16, and one end of the detection rod 29 is connected to the load detector 28. The controller is configured to change or maintain engine operation based on the one or more signals compared to the threshold limits, and to change or maintain an engine fuel supply to control specific fuel consumption of at least one of the first and second fuels and to achieve values for the one or more signals in a determined range relative to the threshold limits.