A falling object, such as a product falling from a magazine to a discharge chute of a vending machine, is detected using a rectangular light curtain having parallel sides. A plurality of light emitters are positioned along one side and a plurality of receptors are positioned along another side opposite the emitters. A timing circuit momentarily illuminates the emitters one at a time at a time while an electronic controller examines the outputs signal from all the receptors. Where one of the receptors fails to receive a signal from one of the emitters an object is presumed to have interrupted the signal. To work properly the electronic controller must complete a cycle of illuminating all the emitters within the time frame that a falling object interrupts the light curtain.