Almost Genius: A Helmet That Stinks When It Needs to Be Replaced

A safety invention geared to selling more bike helmets, with an ingenious form of planned obsolescence.

You can't fault Dr. Christof Koplin for a lack of imagination. An engineer at Germany's Fraunhofer Institute for Mechanics of Material--a clearinghouse for future-forward inventions--Koplin invented a type of foam that actually stinks when it's cracked. The benefit? Koplin suggests bike helmets that tell you when it's time for a new one.

Here's his logic: Bike helmets are supposed to be...