Abstract: An element for detecting combustible gases comprises a catalyst material associated with an electrical resistor serving as both a heater and a thermal sensor, the catalyst material being produced by heating a deposit from an aqueous slurry of alumina, of maximum particle size 0.1 micron, containing in solution a compound of a metal of the platinum group. The deposited material may constitute a pellet (6) within which is embedded a coiled part (3) of a wire (1) constituting the resistor. The element then resembles a conventional "pellistor" in form, but has improved resistance to poisoning or inhibition of the catalyst.