Videos:

How to Build a Laser Security System:

http://www.howcast.com/videos/2947-How-To-Build-a-Laser-Security-System

How to Build a Doorbell:
http://www.youtube.com/watch?v=TMXZmgNu9Hs


How to Build a Burglar Alarm
http://blip.tv/KipkayVideos/infrared-intruder-alert-2345342