Abstract: Detection device for detecting movements by means of a source of light and a photo-detector, which device is provided with: (1) a pulse generator for supplying the source of light with a proportionally very large amount of energy during a very small part of the time; and (2) with a comparator, synchronized with the pulse generator, for comparing a signal received from the photo-detector with the preceding signal during the said time and for delivering a signal to a counter in case a difference is ascertained. The device can be utilized in a manual sorting device comprising one or more sorting-cases. Movements of the upper surface of the stack in a pigeon-hole can be detected by means of reflection. The detection devices in the pigeon-holes are connected via multiplexers and demultiplexers to a central processing unit that has been provided.