A method is disclosed for the protection of catalytic converters for exhaust gas purification by measuring the temperature with a heat tone sensor suitable particularly for the implementation of the method, wherein a heat tone sensor composed of at least two NTC or PTC resistors and provided with a coating of a catalytically active material on the sensor in the region of at least one of these resistors is arranged ahead of the catalytic converter in the exhaust gas stream or a part thereof, with the catalytically active material initiating the same exothermal reactions as they take place in the catalytic converter employed for the exhaust gas purification. If the resistor is overheated due to an overly intensive exothermal reaction, resulting in a change in resistance, the heat tone sensor detects the drop in the throughput rate of the catalytic converter.