A line laser-based light barrier, having a rectangular detection area, consisting of a transmitter and a receiver parts, which are constituted by a line laser and a photodetector array, respectively, is designed. Transmitter is constituted by a line laser, which has a radiation angle of 90 degrees. Line laser is placed in the barrier in order to constitute the two of the edges of the detection area from the line laser beam edges. Receiver is constituted by the serially connected photodetectors arranged vertically and horizontally and constitutes the other two edges of the detection area. Line laser light is directed as to illuminate all the photodetectors placed in the vertical and horizontal edges of the detection area. Design principles of the line laser-based light barrier are given. Calculations for laser light power and geometrical dimensions, determination of total number of photodetectors and the reaction time, a schema and a photograph of the system are given. A receiver circuit consisting of serially connected photodetectors is proposed. Various detection area structures (optical diagrams) are shown. A prototype of the system is realized and the reaction times for different load resistors are found. (C) 2009 Elsevier Ltd. All rights reserved.