This actually looks really cool. It claims to flash a bright light when a camera flash is sensed....
http://www.nophoto.com/
http://www.indiegogo.com/nophoto Kickstarter Page
I have to admit I'm a bit of a skeptic as the timing to sensing a flash and responding has to be faster than the camera shutter. I can also see this going off around police cars or ambulances with their bright flashing lights.... or a car coming around a bend in the dark.
Also the price is high and shipping hasn't started.