How we got our apps ready for iPhone Duo

iPhone Duo folds. Closed, you use the narrow cover screen. Open, you get a wide inner screen. You can switch between the two in the middle of whatever you're doing.

We spent the past few weeks getting Smart Dentist, Smart Billing and Smart Coach ready for it. Here is what changed in the apps, what we tried and threw away, and what we learned.

We started with our own designs, and dropped them

Our first idea was to design for the fold. On Smart Dentist we built two-page layouts: a list on one side and the details on the other, filters on the left and results on the right, two-column grids. We went through six rounds of it.

None of it held up. Splitting a screen into sections left half-empty pages, and the layout jumped every time the phone opened.

So we went back to Apple's own guide, Prepare for iPhone Duo. It is less exciting and much better. Build with the new tools, let the app resize like a window, fix the places where it assumes a fixed screen size, and test it at every size. Apple's goal for the inner screen is that it feels like "a natural extension" of the app's iPad layout.

The same screen in every pose

This became our main rule. When you open or close the phone, you stay exactly where you were. Same screen, same place on it, and anything half-typed in a form is still there.

That sounds obvious, but one of our apps broke it. Smart Billing switched to a sidebar layout whenever the screen got wide. On iPhone Duo, that meant every fold rebuilt the app from the Dashboard, and a half-written bill was lost. Smart Billing now keeps one layout on iPhone Duo, so the bill you start on the cover is the bill you finish on the big screen.

No sidebar: the tab bar stays

On an iPad, a wide screen often means a sidebar. We chose not to use one on iPhone Duo, in any of our apps. The tab bar stays, and pages use the full width.

What changes is where the tab bar sits. On the cover, and on the open Duo held sideways, the system moves it into a narrow side bar along the edge, next to the camera and the status icons. Held upright, it sits at the bottom as usual.

Buttons on the camera line

With the status icons in the side bar, the top of the cover screen is free. Our dashboards have a few buttons in the top corner, like settings. We lined them up with the cover's camera, so they sit on the same line instead of crowding the edge. When you open the Duo they keep that line, and the side bar with the camera stays clear of them.

This also taught us the most common bug. Smart Dentist measured the space at the top of the screen once, when the screen first appeared. On the cover that space is about zero. Opened upright, it is much taller. So after opening the phone, the buttons sat under the status icons. The fix was to measure again every time the window changes. A size you read once goes stale as soon as the screen resizes.

Names wrap instead of "…"

The cover screen is narrow, and long names were cut off on cards ("Aaron Benn…"). We don't like hiding half a name, so on iPhone Duo, names and dates now wrap onto two lines when space is tight.

It turned up in places we didn't expect. In Smart Billing, item rows on a bill still cut off names like "Project Manage…" after we had fixed the lists. Our screenshot pass caught them, and they wrap now too.

We only do this on iPhone Duo. Wrapping everywhere would change how the apps look on small iPhones.

Nothing changes anywhere else

This was a hard rule from day one: getting ready for iPhone Duo must not change our apps on any other iPhone, iPad or Mac.

So we checked. We took screenshots before and after on iPhones running iOS 27 and iOS 18.5, and on iPad, and compared them. The only differences were system details like the clock, and moving effects like animations. On Mac, the iPhone Duo code isn't even included.

The check earned its keep. One change that Xcode's own checks marked as safe moved Smart Dentist's patient cards by 16 points on iPad. We dropped it.

Live Activities on a narrow island

Smart Dentist's Clinic Day and Smart Coach's Coaching Day Live Activities show a countdown in the Dynamic Island. On iPhone Duo, the Dynamic Island runs vertically along the side, so its compact view has almost no width. Our countdown was cut down to one digit: "4…".

It wasn't only iPhone Duo. In iOS 27 the Dynamic Island also stays visible when any iPhone is turned sideways, and there it can't grow wider either. The same countdown was cut off there too.

Apple covers this in the WWDC26 session Live Activities essentials. When isDynamicIslandLimitedInWidth is true, an app should show a short view made for that space, like a symbol, a small gauge or a fixed-width number, instead of squeezing its text. So that's what we did: where the island is narrow, the countdown is now a ring that empties as the session runs down. Upright on a normal iPhone, where the numbers fit, you still see the minutes and seconds, exactly as before.

We checked it on the closed and open iPhone Duo, on an iPhone in landscape on iOS 27, and on iOS 18.5, where nothing changes. The simulator can't rotate a phone or press and hold the island on its own, so we wrote a small automated test that does both and takes the screenshots.

New App Store screenshots

We made a set of iPhone Duo screenshots for each app's App Store page. They follow the iPhone set screen for screen, in every language the page uses, and each one shows the same screen twice: on the open Duo held sideways, with the closed Duo in front.

What we learned

• Start with Apple's guidance before inventing your own design.
• Keep people where they were. Opening the phone should never restart what they were doing.
• Measure again whenever the window changes size.
• Prove that the other devices didn't change, with screenshots, not opinions.
• The simulator can't show the real unfold animation. We will check that on a real iPhone Duo once it's out.

For Smart Dentist, we went through every pose in Apple's iPhone Duo simulator: closed, open flat, open upright, half-open like a book or a laptop, and the moves between them, in light and dark mode and in Arabic.

The Duo-ready versions

Smart Dentist 5.1.1, Smart Billing 5.0.2 and Smart Coach 4.0.2 are our iPhone Duo-ready versions. iPhone Duo goes on sale on 23 October 2026. On every other iPhone, iPad and Mac, these updates look and work just as before.