Abstract: An on the fly optical card reader is provided for reading a card or badge bearing a predetermined number of digits of identifying data spaced in one direction along the card or badge. A guide mechanism guides the displacement of the card past an essentially slot-shaped optical sensing arrangement extending transversely relative to the path of the card and consisting of a light source on one side of the card and a plurality of light detectors on the other side of the card. A correspondingly slotted spring member biases portions of the card on opposite sides of said optical sensing arrangement in the direction of said light detectors. The device is adapted for temporary storage of the output of he optical sensing arrangement and transmission thereof upon detection of the proper passage of the card past the sensor.