i got this off a cool website: diy2345.blogspot.com
Have you ever thought that it would be cool to make your own motion detector? Well now you can with some well written instructions. You need very few parts and the whole thing will only cost a couple of bucks. The parts that you will need are:
2 - Cds Cells (Photocells)
1 - 741 Op Amp
1 - Buzzer or alarm
1 - 9 volt battery breadboard
1 - 10K potentiometer
Not much huh? It really is actually really easy and quick to build. Much more than you would have originally thought. Click on the link for the step by step instructions.