From the audacious to the pragmatic. Or, how iPhones ship.
Way back in January 2015 I wrote about Apple deleting the physical Home button so the company could minimize the bezels in iPhone 8:
Imagine a future iPhone where the screen goes to the edge on both sides, disappearing not at the curve but as the curve. Imagine an iPhone where the FaceTime camera and earpiece take up almost no space, and the screen reaches almost all the way to the top. And imagine an iPhone where the Home button is replaced by some new technology that can still allow for a physical escape to a known state, that can still scan fingerprints and authenticate, but that also lets the screen reach almost all the way to the bottom.
In essence, give people bigger screens without having to give them bigger phones to go with them. Turns out, we got a version of that first with iPhone 7. A non-physical Home button that looked and felt, and forced bezel space, just like the previous one. Back then, though, it felt like the goal was to virtualize and embed the Home button — and the Touch ID sensor that had come to live within it — beneath the screen. That was the next step forward with iPhone 8. (Or whatever Apple calls the next iPhone redesign.)
Back sensor shenanigans
Apple typically has more audacious and more pragmatic prototypes. Like James Cameron says, If you set your goals ridiculously high and it's a failure, you will fail above everyone else's success. Audacity drives what's possible. Pragmatism ensures products ship.
So, everyone might well want a Touch ID sensor all but invisibly embedded in the display or as part of the touch bar, but the realities of the technology, including yield and reliability rates, could force concessions. In this case, it could well force the Touch ID sensor out from beneath the screen and around to the back of the phone.
(Not) only Apple
That's what happened with the Samsung Galaxy S8, according to The Korea Herald:
Samsung Electronics' upcoming Galaxy S8 is unlikely to feature on-screen fingerprint scanning after its touch sensor partner Synaptics ran out of time for developing the related technology, industry sources told The Investor earlier this month.
On-screen fingerprint was a highly anticipated function for the new phone with a larger-than-ever display screen.
"Samsung poured resources into Synaptics' fledgling technology last year but the results were frustrating," a source briefed on the matter on condition of anonymity.
"With the production imminent, the company had to decide to relocate the fingerprint scanning home button to the back of the device at the last minute."
A larger screen that covers almost the entire front body is a key feature for the S8. Since last year, Samsung had made all-out efforts to embed a fingerprint scanner under the display to allow users to unlock the phone by placing their finger on the screen, not the physical home button on the bottom.
But the efforts went down the drain after California-based Synaptics failed to develop the technology on time. As the result, the home button is widely expected to be relocated to the back next to the rear-facing camera lens.
Apple uses its own technology, built on what it obtained when it acquired Authentec just prior to the launch of iPhone 5s and Touch ID. So, Apple may well have succeeded where Samsung and Synaptics did not.
The back is where a lot of Android devices with virtual home buttons have been putting the fingerprint sensor for a while now. It's not my favorite position, though it can be convenient if set high enough that your index finger naturally falls on top of it. If, for security reasons, you prefer to use less predictable fingers, then your convenience will vary. (Samsung actually put it to the right of the camera module, which I'm not sure I'm wild about.)
On iPhone, that should put the sensor right around where the Apple logo is. On iPhone Plus, right around the middle of the phone. Depending on the ultimate size and ergonomics of iPhone 8, perhaps somewhere in between.
Look, don't touch
iPhone 8 is expected to be announced during Apple's annual September product event in California, perhaps at the soon-to-be-completed Steve Jobs Theater. It could well show up with the Touch ID sensor beneath the screen, all right and proper. This schematic might end up being nothing more than some idle speculation about what a less audacious iPhone 8 would look like.
Likewise, the placement of the Touch ID sensor might not be a long-term concern at Apple any more. Touch ID was designed to make security more convenient. Other technologies, include face recognition and iris scanning can do that as well.
Eventually, we might well move towards more passive, ambient authentication. In that future, the answer to where Touch ID goes could simply be: nowhere.