A detector comprises a sensor (5) arranged in a housing (2); and a unit (9) for automatically testing the sensitivity of the sensor and formed by an agent for storing a test substance and for the controlled release of a defined amount of the substance. Preferred Features: The test substance is formed by a solid carbohydrate or a liquid hydrocarbon which is released by heating. The substrate is formed sandwich-like and contains a matrix arrangement. An individually controlled heating element is assigned to each storage position of the matrix.
