Can Zhonya's Hourglass save a unit on a different battlefield than the one it's hidden at?

Ruling: Yes, Zhonya's Hourglass can save a unit on any battlefield regardless of where it is played from, because it is played to base (not to a battlefield) and does not target, so there are no battlefield restrictions on its effect.

Sequence:

• Zhonya's Hourglass is played to base, even when played from hidden
• Since it doesn't target, there are no battlefield restrictions on its effect
• It can affect units on any battlefield

Nuances:

• Gear cards cannot be played to any location except base - they do not have location choices when played
• The hidden rules only limit where units can be played to (must be to that battlefield), but do not create restrictions for gear cards
• When playing a card, units choose a valid location but gear do not make such choices