Abstract: An apparatus for detecting moisture penetrating into a housing having a high-voltage component includes a gas-generating or pressure-generating element which causes gas or pressure to develop when the gas-generating or pressure-generating element contacts a liquid in droplet form. A gas or pressure sensor is arranged with the gas-generating or pressure-generating element in a common envelope element. The gas-generating or pressure-generating element is connected to the housing. The gas or pressure sensor recognizes a pressure increase or gas evolution in the common envelope element and outputs a warning signal.