Abstract: A self-contained photodetector for detecting the light flash from a photoflash unit which is supposed to flash when the shutter of a camera opens. The detector has a light-activated SCR for turning on an IC chip timer, which produces an output signal that turns on a transistor and causes a piezoelectric buzzer to produce an audible signal. All these components are powered by a battery which is contained in the same housing with them. This housing has an opening for passing light onto the SCR.