There is provided a fire alarm device including multiple light sources, a light sensor, a first processor and a second processor. In a standby mode, the first processor identifies whether to wake up the second processor according to a detection result of the light sensor obtained by detecting emission light of one of the multiple light sources. The second processor identifies whether to generate an alarm according to a detection result of the light sensor obtained by detecting emission light of the multiple light sources. The fire alarm device further includes a thermal sensor for providing detected temperature values to the first processor and/or the second processor to perform the identifying procedure.