You can use a screwdriver as a mechanical stethoscope. Put the blade on an engine, then your ear against the handle. Great for tracing bearing knocks, tappet rattles, worn cam chains, etc.
Screwdrivers aren't much chop on gas turbines though, you tend to go deaf, quickly! Mechanical stethoscopes are better there, can even pick up failing ball and roller bearings in gear trains in auxillary gear boxes. Something that millions of dollars of vibration transducers and analysers cant do, they just give you pretty coloured graphs on X-Y plotters.........