How Multiple Displays Work on iPhone Duo
Understand the inner and outer displays on iPhone Duo, and how to build scene-based experiences that use both.
Last updated
Quick answer
iPhone Duo has an outer display for glances while folded and an inner display for full use when unfolded. Most apps only need to support the inner display; the outer display is an optional, scene-based enhancement built on UIWindowScene and best used for small, glanceable content — not a duplicate of your full interface.
Inner & outer displays
iPhone Duo has an outer display for quick glances while folded, and an inner display that becomes available when unfolded. Most apps only need to support the inner display well — the outer display is an optional enhancement, not a requirement.
Scenes per display
Multi-display support builds on UIWindowScene. Each display your app uses is represented by its own scene, so the same multi-window patterns you'd use on iPad — external displays, Stage Manager — extend naturally to Duo's outer display.
func scene(
_ scene: UIScene,
willConnectTo session: UISceneSession,
options connectionOptions: UIScene.ConnectionOptions
) {
guard let windowScene = scene as? UIWindowScene else { return }
if windowScene.session.role == .windowExternalDisplay {
configureOuterDisplay(for: windowScene)
}
}Good use cases
- Now-playing summary while the device is folded
- Glanceable status — timers, scores, delivery tracking
- Camera viewfinder mirroring for the outer display
Pitfalls
Common mistake
Don't duplicate your full primary interface on the outer display. It's a small, glanceable surface — treat it like a complication or widget, not a second full app.
Frequently asked questions
Does every app need to support the outer display?
No. Most apps only need to support the inner display well — the outer display is an optional enhancement for glanceable content, not a requirement.
How is outer-display support implemented?
It builds on UIWindowScene. Each display your app uses is represented by its own scene, so the same multi-window patterns already used on iPad — external displays, Stage Manager — extend naturally to Duo's outer display.
What shouldn't be shown on the outer display?
Don't duplicate your full primary interface there. It's a small, glanceable surface — treat it like a complication or widget, not a second full app.