Laser beams are also being used for perimeter security. Such systems (like infrared beams) consist of a transmitter and a receiver . The transmitter and the receiver are mounted on the wall facing each other. Whenever there is an interruption between the transmitter and the receiver, this activates the alarm.

Like Infrared beams, the disadvantage of such a system is that it may get activated by a cat walking on the wall or a large bird sitting on the wall. To get over such problems, these days there are two or more beams integrated in a single unit. When two or more beams are cut simultaneously then only the alarm sounds. The beams are so far apart that atleast two will get cut by a human being but not by a bird.

The typical distance for such beams is upto 250 meters on a clear night. However, in case of fog or mist or rain the distance is considerably reduced.