You can get these things at hardware stores in the US, but not in central Europe, where the Graffiti Research Lab Vienna operates. Use a light bulb and an electrical socket to create on-the-go power for your tools, in this case a projector.
The basic idea is pretty simple: in a lot of today’s urban environments you can find a regular light bulb reasonably close-by. In Vienna, where this was executed, you can find one above almost every doorstep. The technology is even simpler – take the screw-cap of a regular light bulb and instead of connecting it to filaments it’s being connected to a power socket.