An event sequence detector is described with input units, each associated with a row of bistable elements arranged in an array of rows and columns. The detector also includes a shift register which is responsive to clock pulses from any of the units to sequentially provide signals on its output lines each of which is connected to the bistable elements in a corresponding column. When the event-indicating signal is received by an input unit it provides a clock pulse to the shift register to provide the signal on one of its output lines. The input unit also enables all its bistable elements so that the particular element in the column supplied with the signal from the register is driven to an event-indicating state
