The unending battery→

Smithsonian:

In the mid-1800s, Robert Walker, a physics professor at the University of Oxford, acquired an interesting device. It was a battery designed to propel a hanging metal ball quickly back and forth, between two small bells. Today, 175 years after it was manufactured, the Oxford Electric Bell, as it is often referred to, is still ringing—in fact, it is said to have rung over 10 billion times.

1,000 years from now somebody’s gonna get fed up, crack the thing open, and realize that it’s actually a Tesla-style machine that’s been powering itself off the Earth’s magnetic field.