A device for detecting hydrogen in a gas volume and reducing the hydrogen concentration in an air-hydrogen-gas mixture to beneath the explosion limit, comprising: - a device for the exothermal catalytic recombination of hydrogen in the presence of oxygen in an air-hydrogen-gas mixture for obtaining water; - a device for determining the temperature change that occurs during the recombination; - a device for comparing the temperature change that has taken place during the recombination with a stored limit value; - an output device for emitting a signal, - wherein the device for the recombination of the hydrogen is connected to the device for determining the temperature change that occurs during the recombination in such a way that the temperature change that occurs during the recombination can be determined on the catalyst surface of the device for the exothermal catalytic recombination and the device for comparing the temperature change that has taken place during the recombination with the stored limit value is connected to the output device such that if a stored limit value is exceeded, a signal will be output, wherein several devices for the exothermal catalytic recombination of hydrogen in the presence of oxygen for obtaining water are provided as detection elements, and wherein the output device emits a control signal, by means of which a valve or a ventilation device can be controlled, a common receiving space being provided, in which the detection elements are received, wherein the detection elements each comprise a catalytic pin, a porous ceramic jacket and an absorber space, wherein the catalytic pin is sheathed by the porous ceramic jacket and the absorber space is formed between the catalytic pin and the porous ceramic jacket; as well as a heating device is provided for tempering the detection elements. - a device for the exothermal catalytic recombination of hydrogen in the presence of oxygen in an air-hydrogen-gas mixture for obtaining water; - a device for determining the temperature change that occurs during the recombination; - a device for comparing the temperature change that has taken place during the recombination with a stored limit value; - an output device for emitting a signal, - wherein the device for the recombination of the hydrogen is connected to the device for determining the temperature change that occurs during the recombination in such a way that the temperature change that occurs during the recombination can be determined on the catalyst surface of the device for the exothermal catalytic recombination and the device for comparing the temperature change that has taken place during the recombination with the stored limit value is connected to the output device such that if a stored limit value is exceeded, a signal will be output, wherein several devices for the exothermal catalytic recombination of hydrogen in the presence of oxygen for obtaining water are provided as detection elements, and wherein the output device emits a control signal, by means of which a valve or a ventilation device can be controlled, a common receiving space being provided, in which the detection elements are received, wherein the detection elements each comprise a catalytic pin, a porous ceramic jacket and an absorber space, wherein the catalytic pin is sheathed by the porous ceramic jacket and the absorber space is formed between the catalytic pin and the porous ceramic jacket; as well as a heating device is provided for tempering the detection elements.