My idea was to use the zipper of my hoodie as a switch. When the zipper is open, nothing happens, but when you close the zipper it will close the circuit and power up an IR laser. The infrared laser pointer is equipped with an interchangeable lens that would turn the laser beam into a text or a picture that you could project to a wall. This IR graffiti would be invisible to the naked eye, but security cameras and digital still cameras would be able to see it.
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