QR codes are 2-dimensional barcodes that can store quite a bit of information, like website addresses and SMS messages. Best of all they can be easily scanned by any smartphone with one of dozens of free QR scanning apps.
I've seen several methods for creating spray paint stencils of QR codes that require CAD software and CNC routers. I've come up with a much simpler method you can do in a couple of hours.
Step 1: Assemble Your Parts And Tools
1. Fence wire (or chicken wire) with square holes.
- You can find this kind of fence wire at most any hardware store. It's sold cheap and by the foot. The size of the square holes range anywhere from 1/16" up to 1/2", allowing you to make many different QR code stencils in many different sizes. In this instructable I'm using 1/4" fencing.
2. Masking tape (the wider the better)
3. Xacto knife (#11 blades recommended)
3. Pliers for cutting wire (the smaller the better)
4. Two sharpies of different colors.
5. Black spray paint
Step 2: Create Your QR Code
You can also use RACO Industries' QR Code Generator to add a level of error correction if you're worried about the final piece being readable. I did not have this problem though, even with the crappy stencil I spray painted.
Now count the number of pixels along the perimeter of the QR code so you know what size to cut the fencing to later on. Since this is just a simple URL code it is 25px by 25px.