Electric VF photojammer

I have seen the VF photojammer advertised as being set off when a camera tries to take its photo. How does it work during the day when the camera doesnt use a flash? Or does it only work at night? If it does go off during the day ,will the light it shines on the plate have any effect?
Has anyone here tried them?

Actually the light suppose to be so brilliant that it would work in tha day also,what im wandering is how long does this bulb last.