TiO2 sol–gel films doped with gold nanoparticles are used as both optical and conductometric sensors for the detection of CO and H2. Tests performed at 360 °C show for the first time CO- and H2-induced reversible variations in the optical absorption of thin TiO2/Au sol–gel films. The absorbance changes are strongly dependent on both the testing wavelength and the film microstructure. Together with the sensing dynamics observed through an electric interface, it is possible to obtain a better understanding of the mechanisms involved in the detection of both gases. The presence of H2 elicits almost ideal, step-like dynamic responses using conductometric detection.