A method of detecting a fire condition in a monitored region includes concurrently monitoring the region by a first sensor sensitive to radiation within a first bandwidth which includes the CO.sub.2 emission band, by a second sensor sensitive to radiation within a second bandwidth which includes wavelengths mainly lower than the CO.sub.2 emission band, and by a third sensor sensitive to the radiation within a third bandwidth which includes wavelengths higher than the CO.sub.2 emission band. The measurements of all these sensors are utilized in determining the presence or absence of the fire condition in the monitored region.