My laser trip-wire security system employs a programmable combination lock that acts to arm and disarm the system, as well as indicate to the microprocessor if someone has entered in a faulty code (Tampering). There is also a really awesome and LOUD Siren with strobing indicator LEDs. The laser trip-wire is bounced across several carefully aligned mirrors and back to the laser detection circuit. The costs to create this project are pretty low. The only real cost is in the siren ($19) , the LS7222 ($6), and the keypad ($5).
Aligning the mirrors was the most difficult part, as I had to purchase sticky tack to stick them to the wall, and to be able to adjust the mirrors in different directions. The sticky tack kept moving over time, which made it extremely difficult. However, patience persevered, and I was able to get a nice video demonstration. I was able to purchase the Mirrors and the sticky tack at the local dollar store!
If there was more time, I would have added an extremely sensitive laser detection circuit, and a battery backup but instead I've added these schematics and instructions into the EXTRAS section so that you can use them in your future projects. I've posted three videos relating to this project::
1) A demonstration of my design with the mirror set-up that I have in my hallway.
2) A breakdown video of the electronics involved for those of you who don't want to have to read through the electronic block sections of this instructable.
3) A second up-close demonstration of the system with an explanation of the program algorithm.
I have worked extremely hard to offer as much detail as humanly possible regarding each aspect of the electronic hardware. I've included copies of thoroughly commented software, and a block diagram of the program algorithm.
For the better part, I don't expect anyone to fully re-create this project, but I have detailed so much information that the viewer will be able to use many blocks and schematics, or variations of them in their own projects. Thanks for viewing. As always, I appreciate your comments and perhaps your votes, if you find I deserve them =)
I've designed and implemented this model into a DIY kit. While I haven't integrated it yet, it will be available at www.engineeringshock.com and www.electroniclessons.com (Ebay Store) By mid February 2013. It will include the circuit, a pulsing siren, and an AC adapter. Below is the demonstration video: