<p>An improved fire alarm system capable of reliably detecting the presence of fire caused by different sources. The fire alarm system detects a smoke density (S) as well as a temperature difference ( DELTA T) within a predetermined time interval, and has primary criteria of (i) whether the smoke density (S) exceeds a smoke threshold Äe.g., S>5 %/mÜ; (ii) whether the temperature difference ( DELTA T) exceeds a temperature difference threshold Äe.g., DELTA T>/=18 CÜ; and (iii) whether a combination of S and DELTA T satisfies an inequality Äe.g. 2S + DELTA T >/=12Ü which is based upon a decreasing function of DELTA T with an increase of S. The detected smoke density and the temperature difference are examined with reference to the primary criteria so as to provide a fire warning signal indicating a possible fire presence when anyone of the above primary criteria is satisfied. <IMAGE></p>
