In a really strange brainstorming session, a friend and I came up with the unique idea of creating a system that would detect whenever someone's zipper is down. We decided to enter this into the Zip It Good! Contest on Instructables.com and we wanted to share it with the Hackaday world.
My MattDougan and I approached this problem with two approaches. I used two photodiodes, one placed towards the top of the fabric behind the zipper and the other placed towards the bottom. An LED is attached to the zipper tab. When the zipper is pulled downwards or upwards, the photodiodes are triggered. When a "zip down" is detected without a corresponding "zip up" event, a haptic response is triggered alerting the user that their zipper is down!