"The partisans have unearthed a strange artifact. None know its origin, but it gives them hope of a life beyond."
—Elspeth's journal

Unwinding Clock

Untap all artifacts you control during each other player's untap step.

The Brothers' War Retro Artifacts

"Heat from the rotating mechanism is captured and converted into energy, allowing it to operate in perpetuity."
—*Rusko's Compendium of Clockwork*

The List

Commander 2018

Even if you control more than one Unwinding Clock, you'll only untap your artifacts once during each other player's untap step.

Some effects, such as the one generated by Rust Tick's ability, state that an artifact doesn't untap during its controller's untap step. These effects won't apply and stop the artifact from untapping during another player's untap step.

Those artifacts untap at the same time as the active player's permanents. You have no choice about what untaps and can't choose to not untap an artifact you control.