The iPhone Duo

Each side of split screen acts like its own iPhone Duo. Drag up from the bottom of a side and you can go back to the home screen on that side. Or, as shown above, you can enter the multitasking switcher interface on that side — and it’s smart enough not to show you the app that is already open on the other side. Drag up from the bottom center and you return to the full-screen home screen or full-screen app switcher. Whatever you think ought to work, probably works. That’s intuitive design.

There is more to explore and think about here. These are not “windows”. But you can open the same app on both sides, like to show two Safari pages side-by-side. What this split screen UI gets fundamentally right is that it works exactly like using the iPhone for one-app-at-a-time launching and switching. The iPad’s original split-screen sin was trying to implement multiple apps on screen at the same time when the iPad still used a hardware Home button. With the modern iOS UI, where the physical Home button has been replaced by virtual on-screen home indicator bars, you can go from one home indicator (when there’s only one full-screen app) to three: one for the app on the left, one for the app on the right, and a third in the center to control them both as a pair. It’s so brilliant that most users won’t notice that there’s anything clever about the design at all. They’ll just use it. That’s the highest praise for an interaction design like this. It seems so obvious that it doesn’t seem designed at all.

Ironically, because iPhone Duo is not called an “iPad”, it gets to be what the iPad should’ve been all along.

The biggest problem I have with using the Duo on the inner display is an incorrect intuition that, after a full week of use, I am only now starting to break. What do you do when you’re done with a book for now? You close it. So what do I do when I’m done using the iPhone Duo, unfolded, before putting it in my pocket? I close it. But that doesn’t lock the Duo. It just switches to the outer display. I feel like I’ve done this a hundred times in the last week. I close it, thinking that I’ve locked it, and I put it away. But it’s still open. It eventually locks — perhaps sometimes quicker than you think. (iPhones have long used a bit of machine learning to try to detect when they’ve been pocketed or pursed while unlocked, and lock themselves before the normal auto-lock timeout.) Nothing bad has happened from doing this. But I’ve opened it up to some odd things on screen. This is not a complaint about Apple’s design, because when you want to switch from using the inner display to the outer display, you should be able to just close it. The iPhone Duo can’t read your mind. But I wish it could read my mind.

The lack of Face ID on the iPhone Duo is an endless unceasing frustration. I’ll just farm this section out to what I wrote back on September 15, days after the Duo was announced, in my thoughts and observations column on Apple’s event announcements:

The lack of Face ID is a serious sad-trombone bummer, and in my opinion could sink the first-generation model. Side-button Touch ID is OK, but OK is not good, and even good is not insanely great. Face ID is insanely great. For whatever reason, the only iPads with Face ID are the iPad Pro models. Every time I review an iPad Air or iPad Mini, my biggest gripe is the lack of Face ID. I complained about it reviewing the iPad Air in 2022 and the iPad Mini in 2021, and in the five years since then my annoyance has only grown. With Face ID, so long as you’re looking at the screen as you unlock the device, it’s like not having it locked at all. It just unlocks, seemingly automatically. With Touch ID you must think about putting one of your registered fingers on the button every single time you unlock it. It never ever feels automatic. I feel quite certain Apple tried to fit a Face ID sensor on the outer Duo display and could not make the engineering work.

I’m much more concerned about convenience than security, but Face ID is 20× more secure than Touch ID. That’s according to Apple’s own Apple Platform Security whitepaper, updated just last month, which states:

The probability that a random person in the population could unlock a user’s iPad, iPhone, or Apple Vision Pro is less than 1 in 1 million with Optic ID or Face ID — including when Face ID with a mask is turned on. For a user’s iPad, iPhone, Mac models with Touch ID, and those paired with a Magic Keyboard with Touch ID, it’s less than 1 in 50,000. This probability increases with multiple enrolled fingerprints (up to 1 in 10,000 with five fingerprints) or appearances for Face ID (up to 1 in 500,000 with two appearances).

As a sign of how inconvenient the lack of Face ID is, Apple is promoting the fact that the iPhone Duo can be unlocked by your Apple Watch, like a Mac. No other iPhone needs such a crutch. Based on my experience with Touch ID iPads, wearing an Apple Watch all the time to unlock the Duo will feel essential. I don’t wear an Apple Watch all the time, and don’t want to start wearing an Apple Watch all the time, so I suspect this alone will keep me from switching to an iPhone Duo personally. On the other hand, for people who do wear an Apple Watch all the time and are happy to do so, the Duo’s lack of Face ID might prove to be only an occasional inconvenience rather than a constant annoyance.

I’ve seldom been more prescient. More than anything else about the Duo experience, I despise the lack of Face ID. It is a dealbreaker for me. I’ll reconsider a future model that at least has Face ID on the front outer display, but I have no plans to purchase this one. I tried to keep track in my pocket Field Notes notebook how many times I had to be told to authenticate with Touch ID, along with a separate tally of how many times I had to enter my full device passcode in situations where I know I would not have with an iPhone uno, and I ran out of space on the sheet of paper. If you are not wearing an Apple Watch, it is an unceasing frustration.

Apple actually made a TV commercial exemplifying the Touch ID experience on iPhone Duo 20 years ago, as part of the “Get a Mac” campaign with John Hodgman and Justin Long. Here, you can watch it on YouTube. Over and over and over, seemingly 20,000 times a day: put your goddamn finger on the Touch ID button.

Now, if you do wear an Apple Watch, and you pair it with your iPhone Duo, and you enable the off-by-default setting to allow your watch to unlock your Duo, this is much better. It’s not good, but it’s at least tolerable. If you have multiple iPhones though, this feature only works if your watch is paired with your Duo. This is a fundamental shortcoming in the architecture of WatchOS. Apple Watch should be like AirPods, where it just pairs on-the-fly with whatever device you’re currently using, so long as they’re signed into the same Apple Account. You don’t have to pair your AirPods to one single device and then completely factory reset them to use with another. AirPods wouldn’t be a hit product if that were true. But that’s how Apple Watch works. It’s true that most people only own one iPhone, but the existence of the iPhone Handoff feature is proof that Apple is thinking about the fact that some of us own more than one. If one of them is a Duo, you will want to pair your Apple Watch with the Duo. But that means that with iPhone Handoff, your Apple Watch won’t share a cellular connection when you’re using your other iPhone. Cellular carriers are now more adept at seamlessly dealing with multiple iPhones than Apple’s own watch. It’s a complete mess of Apple’s own making.

The unlock-with-Apple-Watch feature doesn’t work all the time for me. When it does work, you know it, because you get a tap on your wrist from the watch every time your Duo unlocks via the nearby watch. But sometimes, even though I haven’t taken my watch off since it last unlocked the Duo, it doesn’t work, and I have to use Touch ID. Oftentimes, for reasons I do not understand, Touch ID isn’t enough, and I have to enter my passcode. I think it’s because I so often inadvertently press the side and Camera Control buttons while folding and unfolding the Duo — that might put it in a state where it wants to authenticate the most secure way possible, with my passcode.

It’s mildly annoying that your Apple Watch taps your wrist every time it automatically unlocks your Duo (dozens and dozens of taps per day, every day), but it’s obviously a good thing that it does. It obviously is less secure than Face ID or even Touch ID. I handed the Duo to my son to play with the hinge over the weekend, and as soon as he started playing with it, my wrist tapped. Oops, the whole iPhone was unlocked for him. That was no big deal, and in fact we shared a laugh about it. But it couldn’t happen with Face ID or Touch ID.

There’s also an optional feature where you can unlock the Duo just by “resting” a registered finger on the Touch ID button. This does add a touch of convenience (again, I swear no pun intended), when I remember to do it, but this too doesn’t seem to work all the time. My theory is that sometimes I’m resting my finger on the button and the sensor doesn’t think the finger is a match. Other times, I wind up unlocking the Duo inadvertently, just by holding it with my thumb on the button. I never ever unlock my iPhone Pros accidentally. With the Duo, it happens at least once a day.

The only tolerable way to use the Duo is by always wearing an Apple Watch, and enabling the feature to allow the watch to unlock it. I do not want to wear an Apple Watch all day every day. And it seems ridiculous that that’s the only way to make the Duo experience tolerable. As annoying as it is to use an iPad with a Touch ID button, it’s far more annoying to use an iPhone with one, because I unlock my iPhone at least an order of magnitude more frequently than I do my iPad.

I’ll reconsider a future Duo model that at least has Face ID on the outside, but I don’t think I’ll ever truly enjoy the experience of using one unless it has Face ID on both sides. I can’t wait to finish writing this review, switch my eSIM back to my iPhone 18 Pro, and set this Duo aside on my desk. I don’t think Apple should have released the Duo until they figured this out.

My Touch ID complaints are exacerbated by the fact that, from an experiential standpoint, the side button keeps moving around. When the Duo is closed, button placement isn’t a problem. But when it’s open, the buttons feel wrongly placed. On a Touch ID iPad, held vertically, the button is on the top on the right side. And from there, to switch to horizontal orientation, you rotate it counterclockwise, which moves the Touch ID button to the left side, at the top. But this is all backwards on the Duo. Held vertically, the Duo’s Touch ID button is on the top on the left side. And you have to rotate it clockwise to get it back to horizontal. I’ve gotten more used to it after a week, but while using the big inner display, whenever I’m pestered to authenticate with Touch ID — which, again, is all the time — there’s also a moment of “Wait, where is the Touch ID button?” Many times throughout the week, while holding it vertically, the Touch ID button has been on the bottom, because my instincts for how to rotate it from horizontal to vertical and vice-versa are backwards from how the Duo intends. It’s like the Duo has a built-in game called “Where Are the Buttons?”, and it’s not a fun game.

The main camera orientation is more frustrating, and I consider it a mistake. The main camera is aligned with the small outer display. When you’re capturing photos or videos using the outer display, you hold the Duo horizontally to capture horizontal images, and hold it vertically to capture vertical images. But when you open the Duo, the camera sensor doesn’t magically rotate. So when you’re using the big inner display, you capture horizontal images when holding the Duo vertically,