An infrared detector has at least one infrared-sensitive detector element and at least one infrared source disposed in a common housing with the detector, with the infrared radiation from the source being directed onto the detector element. A pulse generator is connected to the infrared source for pulsing the infrared radiation therefrom. A recognition circuit is connected to the detector element for identifying the pulse sequence of the detector output so as to continuously check the functioning of the detector. A number of such detector elements can be arranged in the housing, with each detector element having a respective infrared source associated therewith. The infrared source may be a heated wire, a chip resistor, or a light emitting diode.