Kundo 'electronic' Induction Clock
The pendulum is made from a magnetic material. As it swings, it moves through
the coil, generating a small electric current.
This current is amplified by a transistor and fed back to the coil, giving the pendulum a small push every time it passes.
These clocks can run for years on a LR20 battery. As the battery goes low, the amplitude of the pendulum gradually decreases first.