Abstract: An electro-optical detection system for detecting objects within the boundaries of a monitored zone, comprises a plurality of LED emitter and photodetector pairs. Each emitter (12) emits a beam of pulses of light energy into the monitored zone, and its paired photodetector (14) detects light energy including light energy from the beam that is reflected from an object within the monitored zone and generates light detection signals. A controller (10) operates the emitter and photodetector pairs and evaluates the light detection signals to discriminate between light energy of beams reflected from an object within the monitored zone and other light energy. The controller can selectively adjust the evaluation of the light detection signals to adjust the effective boundaries of the monitored zone.