An infrared-detecting device, includes an infrared detector configured to emit a signal representative of the thermal radiation of a hotspot, and a light source configured to emit an incident beam, preferably in a window of UV or visible wavelength. The infrared-detecting device furthermore comprises a synchronizing device connected to the light source and to the infrared detector or to the processing module, and configured to emit a synchronization signal, the infrared detector being configured to be activated in a preset time window depending on said synchronization signal.