This invention discloses a method for detecting the presence of a moving object in a detection area, including emitting a sequence of bursts of ultrasonic energy into the area, receiving ultrasonic energy reflected from within the detection area, in response to the sequence of bursts, and generating a sequence of signals respectively responsive thereto, comparing each signal in the sequence with a preceding signal, to find a variation in the signals over the sequence of bursts, and analyzing the variation in the signals to determine the presence of the moving object. Apparatus for detecting the presence of a moving object in a detection area is also disclosed.