How do you know when your car tires need to be replaced? You could eyeball it, you could guess, or you could wait until they shred off your rims while you're barreling down the highway, flinging mangled rubber across a two-mile stretch of asphalt and depositing your car in a ditch.
Alternately, Duke University engineers and the Fetch Automotive Design Group have figured out a way to sense the wear of car tires down to a fraction of a millimeter to determine if it's in need of replacement. This technology already existed in expensive forms; in fact, there's a $2 billion tire and wheel sensor market. But these electrical engineers discovered how to do it inexpensively, and they used 3D printing to do it. This could mean that future cars will have built-in tire sensors, saving time, money, and even lives.