Abstract: An electronic watch having a case and a case back, a digital display, an integrated circuit, a battery and a fixed photo-electric pick-off placed on the module facing a window. The pick-off is for preference a photo-diode and its functioning is controlled by obstructing with a finger the window so as to prevent the ambient light from lighting the pick-off. According to the invention, the control system of the watch has the advantage of being insensitive to electrical parasites, of consuming little current, of being only slightly dependent upon the intensity of ambient light and of being simple to fabricate.