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See this bike helmet? No? That's because it's invisible. No, really, it is: that hefty collar that the bicyclist (or whatever) in the above pic is wearing contains a helmet-shaped airbag that deploys on demand to save your skull, and spends the rest of its time out of the way and looking fashionable.
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The Hövding (that's "chieftain" in Swedish) took seven years and $10 million to bring from concept to product, but unlike most things that are invisible, it's finally out there for purchase: you can buy a Hövding of your very own for just four of these bad boys:
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That works out to about 4,000 Swedish kronor, which sounds like a lot, and equates to just under $600 USD, which also sounds like a lot. But remember, you're not paying for a helmet, you're paying for lack of a helmet without compromising your safety. And also, you get a free neck warmer. So it's totally worth it. And if you're still not sold, there's a video of the Hövding in action below.
Hovding, via Core77