The present invention relates to a registering device for registering a location along a measuring line, at which location a temperature change takes place. In an advantageous way, according to one exemplary embodiment of the present invention, by means of the FMCW method a location on the measuring line is determined, at which location a temperature increase exceeds a predefined threshold value. The location is determined on the basis of a signal which is registered by the measuring line in response to a fed-in frequency modulated signal from evaluation electronics. Advantageously, in this way a simple and lightweight overheating warning system is provided, for example for hot-air supply pipes in aircraft.