Abstract: The invention relates to a device for long-term leakage monitoring, in particular of flat tank structures, comprising a sensor cable arranged on the outer surface of the tank casing. A collection chamber which, with respect to its height, is arranged at least partially below the bottom of the flat tank structure, surrounding its circumference preferably in an annular manner, and which via an inclined cantilever is connected with the lower end of the outer surface of the tank casing, with the sensor cable being arranged on the cantilever or in the bottom area of the collection chamber. According to the invention, a fire signalling sensor is located above the collection chamber which, in the case of a fire, in cooperation with an extinguishing supply, enables the activation of the automatic foaming of the collection chamber.