Smoke and gas sensor element

In a method for detecting the presence of smoke and/or a gaseous substance in an atmosphere, comprising bringing the atmosphere into contact with a sensor element, whose resistance changes with the presence of said smoke and/or gaseous substance, and measuring the resistance of said sensor element while said atmosphere is in contact therewith, the improvement wherein said sensor element is formed from a material comprising (1), a complex metal oxide having a perovskite type crystal structure and represented by the general formula ABO.sub.3-.sub..delta., wherein A is at least one element selected from the group consisting of yttrium, a rare earth element of an atomic number from 57 to 71 and an alkaline earth metal, B is at least one element selected from the group consisting of transition metals of the atomic numbers from 21 to 30, O is oxygen and .delta. is a nonstoichiometric parameter, and (2), at least one metal oxide selected from the group consisting of CdO, In.sub.2 O.sub.3, SnO, Tl.sub.2 O.sub.3 and PbO.

A sensor element for detecting smoke and/or reducing gases, which comprises a shaped body or layer formed from a material consisting essentially of a mixtue of:

• A. a complex metal oxide having a perovskite type crystal structure and represented by the general formula ABO.sub.3-.sub..delta. wherein A is at least one element selected from the group consisting of yttrium, a rare earth element having an atomic number of from 57 to 71 and an alkaline earth metal, B is at least one element selected from the group consisting of transition metals having the atomic numbers from 21 to 30, O is oxygen and .delta. is a nonstoichiometric parameter which may vary from 0 to 0.25 and
• B. at least one metal oxide selected from the group consisting of CdO, In.sub.2 O.sub.3, SnO, Tl.sub.2 O.sub.3 and PbO.