A Zipper is a great clothing material that can be converted into sensors. Zipper switch is a known technique used in many projects like TV-B-Gone-Hoodie by Becky Stern. It is also introduced in “Fashioning Technology” book by Syuzi Pakhchyan.
There is a great tutorial from ITP here >> http://itp.nyu.edu/physcomp/sensors/Reports/ZipperSensor

Anyhow, I had to make one of my own. so I did it. And yes, it works very good and it is relatively easy to make. I have fused stretchy conductive fabric next to the zipper line on both side of the zipper. The zipper used here is not metallic except the zipper head, therefor the zipper head has to touch the fused conductive fabric directly. I have sandpapered the zipper head to remove the paint so that the metal inside touches the conductive fabric directly. As you move the zipper head, it makes an electronic connection between the conductive fabric through the zipper head. The switch is “ON” while the zipper head is on the fabric, and it is “OFF” as it goes out of the fabric.