Security is main concern for various buildings, houses and offices. For this purpose, there are a variety of security alarms available in market which uses various types of technology for intruder detection like infrared sensors, motion sensors, ultrasonic sensors, laser sensors, etc. We have also built some security alarms like this PIR sensor based motion detector and burglar alarm circuit. In this circuit we are going to build a laser security alarm which uses a laser light and a laser light detector circuit. It gets activated when someone crosses it.