Wearing a helmet whenever you go out on a bike is mandatory, since it offers you a degree of protection just in case of an accident. Unfortunately, one also ought to make regular checks on your helmet just in case it has aged beyond its intended purpose, which is why a bunch of boffins over at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg came up with a new process for the manufacturing of bicycle helmets. This process relies on micro capsules that are filled with a odor-causing oil during production, while a layer of melamine formaldehyde resin encloses the capsules in order for them to remain completely airtight and mechanically sealed. Should a knock heavy enough hit the bike helmet (or it has aged sufficiently), the microcapsules will break to release a stinky odor, making sure your nose won’t be able to stand it at all, and hence, forced to buy a new helmet.
Source: Geeky Gadgets