We’re going a bit specialised here on Red Ferret today, but I think you’ll cope. These are SmartBolts, they tell you when they’ve been tightened sufficiently and when they haven’t. The little coloured dot on the head changes colour as the bolt is tightened, red for undone, black for correctly tightened. The visualiser works by compressing a small compartment filled with fluid so there are no moving parts and the bolts will last +20 years.
There’s also a high resolution version will show you when the bolt has been over tightened and bolts can be manufactured in M10 to M32 sizes. Great idea.
No wires, instruments, complex procedures or electronic black boxes. The only instrument needed is the eye. The indication is based on the most accurate known principle for fastener tension measurement – actual fastener elongation under load.