The good news is that you don't have to anymore. The LucidBrake is here.
Bikes need brake lights when riding around anyone else - be it a car, another bike rider or a pedestrian. So many accidents can be avoided with the simple use of this brake light - so many hospital visits can be avoided.
Old brake lights needed wiring and alteration of the bike. This either nullified warranties or just plain intimidated people who didn't want to mess with their braking systems. Well, the LucidBrake's wire-free and press-on features eliminate that concern. No more altering of your bicycle. In fact, don't put it on your bicycle at all... Put it on your helmet!
That discussion is worthy of another post!