Diy100-1
Max writes – “Here’s a DIY on how to make an alarm system in 3 minutes. We will use a loud buzzer and some magnetic switchs from Radio Shack to create a simple yet effective alarm system. We will throw in a LCD, keypad so we can alarm the alarm system using a 4-digit code and be able to see the system status using the LCD.” – Link.

Related:
HOW TO – Build an ultrasonic burglar alarm – Link.