to make it work you replace your regular brake light with a special one that also send a radio transmission up to the helmet, turning that light on whenever you brake.
a problem i can see, if you ride next to someone, might not their brake light also turn on your helmet light is signals get mixed?
what if the biker turns to look at something. won't know which way he's going.
//a problem i can see, if you ride next to someone, might not their brake light also turn on your helmet light is signals get mixed?// use the same technology as car remotes to lock the two units (link). in theory 