Machine-gunners use tracer bullets to see whether they are on target – but the tiny, glowing incendiary devices can be seen from all directions and reveal where the fire is coming from.
Harry Rector and Robert Burruss have a better idea (US 2004/99173). The light in their tracer round comes from a rearward-facing LED, so only the gunner can see it. It is powered by a capacitor, which in turn is charged up by a piezoelectric crystal that generates a pulse of electricity as it is shot out of the gun barrel.
