A laser fence is a mechanism to detect objects passing the line of sight between the laser source and the detector[1]. Stronger lasers can potentially be used to injure someone or something passing the laser beam (see mosquito laser[2]).
Sometimes laser fences are used in fiction with the ability to stop intruders by blocking or injuring them. It is a concept used frequently in videogames[3][4]. The concepts of these fictional fences can be compared to other concepts like tractor or repulsor beams.