The proposed smoke sensing element is a thin film of bismuth sesquioxide made by different deposition methods by use of a corresponding hear treatment, The resistance of thin films placed in smoke medium is changed by about five orders of the magnitude at room temperature. The film's influence on neutral and charged solid smoke particles on the thin film resistance was investigated. It is shown that the contribution of the particles on the resistance is negligible up to 30% of the smoke concentration in air and the sensitivity of the samples investigated is caused by gases, formed by the combustion.
