This is one of those stories that is part "why didn't someone think of this before" and "you've got to be kidding, it's not April fool's day"
New technology has been developed that lets you know by smell if your helmet needs to be replaced. I'm not refering to that particular "funk" that helmets tend to pick up when they aren't washed regularly, but to when you fall and your helmet strikes the ground.
Helmets can be expensive, We are told to replace our helmets if they are involved in an accident, or are damaged. But if there is no outward indication of damage, that can be a tough judgement call.
The Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, Germany has developed a new technique that uses encapsulated polymer materials or plastics that are filled with odoriferous oils. If your helmet is damaged, the capsules are ruptured producing a noticable stench. The more damage done, the more capsules ruptured, and the worse the stench.
The capsules are added to a polypropylene mass, which is injection-molded to form the final component. In the case of the bicycle helmet, the microcapsules are inserted in a thick foil made of polypropylene, which is fastened to the headgear. A layer of melamine formaldehyde resin encloses the capsules so that they are completely airtight and mechanically sealed.
I wonder how long until we see helmets hit the market with this technology.