Abstract: A device for detecting thermal radiation having a detector and a reflector type concentrator. The detector is arranged to have one or more portions exposed to thermal radiation and one or more portions protected from thermal radiation, wherein the detector delivers detection signals on the basis of a temperature difference between the exposed portions and the protected portions. The detector supports pairs of planar thermocouple elements having a cold junction in contact with the protected portion of the detector and a hot junction in thermal contact with the exposed portion of the detector. The reflector type concentrator concentrates thermal radiation coming from a three-dimensional zone. The detector and the reflector type concentrator are combined to define a zone under surveillance and detect any change in the state of thermal unbalance in the zone under surveillance.