Using relatively simple technology, Mr. Chuck Popenoe has invented something with a high-tech aura: the Smartbolt.
This device is simple, low cost, highly accurate, reliable, reusable, and best of all, highly visible. This visibility comes from the indicator contained within the bolt.
Using some relatively simple physics, the components of the indicator do their job by selectively absorbing and reflecting light as it passes through. The result is nothing short of cool as tightening and elongation of bolt as it threads in, changes the geometry so that the color changes. The animation on their webpage is fun as you can tighten a virtual bolt and watch the color change.