We've gone over this before (Boy have we!).
Many cite junk science claiming there's no real safety benefits to wearing a helmet on urban streets (silly). And then there are those who admittedly forgo the protection for vanity. They just don't like how helmets look and feel.
For the latter group (there is probably no helping the former), two Swedish women have invented Hövding -- the "invisible bicycle helmet." It looks like the top of a hoodie, but acts like an airbag when there's a collision. (To your left, the Hovding inflatable bike helmet/airbag -inflated)
Lund University students Anna Haupt and Terese Alstinat had to overcome sexism, funding challenges (they eventually raised $10 million) and years of setbacks to develop the non-helmet.
Along the way, they received help from a trauma specialist, the Swedish academic community and scores of bicyclists who were tired of wearing what one inventor calls "a hard mushroom on your head."
You can now buy an invisible helmet, which uses accelerometers and gyroscopes to detect when a bike crash is in progress.
However, this new way of protecting your noggin is not cheap: The price is $600 and it only works once. Still, you can bike to work or the grocery story with the wind in your hair, without worrying about cracking your head open if you're hit by a car. (Plus, it is cheaper than most healthcare deductbles?)
Of course, it should also been noted that there have been some complaints about zippers coming undone in crashes.
GE has produced an excellent video telling the story of the Invisible Helmet. If you don't mind reading subtitles?