Laser beams are forms of modern security items place on a straight line (line of sight) facing each other. Space between creates an unseen barrier which when crossed triggers an alarm. Space can be as from 1metre to 100 meters, depending what area you want to protect.
This system can be linked to your alarm system and security lights such that in case of an intrusion the alarm is triggered, siren, and the security lights come ON.
Mostly they are used as the second layer of security after the physical wall or the electric fence.
This too can be linked to the GSM system which sends you a notification message wherever you are, then you can take action. Cool, right?