A method is provided for cleaning an optical entry window (1) of a fire detector (2), wherein an intermittent gas stream is discharged from at least one gas exit opening (7) onto the surface of the optical entry window (1) of the fire detector (2), wherein the intermittent gas stream having a number of pressure pulses (14) is discharged onto the optical entry window (1), and to an apparatus for cleaning an optical entry window. The method has the advantage that the optical entry window of a fire detector can be cleaned from contamination intermittently and corresponding to the intensity of contamination with a matched and low consumption of gas.