Finding a way to embed a fingerprint scanner into the display of your handset is seen the holy grail of smartphone biometrics. As phone makers push relentlessly towards the vision of "full-screen" devices, in-screen fingerprint provides yet another way to bump up that all-important screen-to-body ratio.

In-screen fingerprint also offers a futuristic edge -- a much-needed differentiator in a homogenous marketplace of interchangeable, commoditized glass slabs.

So it's no surprise to have seen this burgeoning technology cropping up in supply chain rumors around future devices, particularly concerning the two biggest players in this industry: Apple and Samsung. It's been a couple of years since we first heard whispers of a full-screen Galaxy handset with a fingerprint scanner in the display. Indeed, Samsung's current button setup, with a pressure-sensitive virtual clicky home key, seems to have been designed around this concept.

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Yet so far, outside of a few concept devices from China, it has failed to materialize.

That's why, going into my review of the Porsche Design Huawei Mate RS, the thing most alluring to me about this $2000 handset was that, finally, someone was shipping a flagship phone fingerprint behind the display.

My enthusiasm, however, evaporated within minutes of actually using the feature. The process of registering fingerprints in the in-display sensor hammers home just how slow the new sensor is compared to the capacitive fingerprint tech we've been using for the past several years. We've been spoiled by effortlessly quick fingerprint scanners in smartphones for the past few release cycles. In-screen fingerprint, at least as it's implemented in the Mate RS, is like going back to a fingerprint scanner from 2014 or 2015, with waits of up to a second to unlock.

There's no reason to suspect Huawei of cheaping out in a phone that goes for up to $2600 in the markets where it's sold. The company is surely using the best components available to it. But those components are slow.

There are also practical issues. Since it's an optical sensor, which has to actually see your fingerprint to scan it, the phone has to light up the area around the sensor as you press. That's fine in daylight. In a dark bar or bedroom? Annoying.

In 2018, in-screen fingerprint is a tech demo: Functional, but slow and unreliable.

On the Mate RS in particular, it also takes time to find the in-screen sensor and press it. (Current optical sensors require pressure to work properly, as the sensor needs to see a flat image of your fingerprint.) Given that the sensor is about a quarter of the way up the display, it's not somewhere that's easy to find by touch alone -- since the sensor in is in the screen, you can't feel where it is. In addition, there's also no haptic feedback to guide you. Instead, you'll need to look at the device, and find the telltale glowing target.

And once you've done that, you in most cases you might as well have used Huawei's excellent face unlock feature, which is quicker and more reliable.

Even after registering four fingerprints on the Mate RS, I ran into way more hiccups than I have from a traditional fingerprint scanner in at least three years. On some occasions, no amount of repositioning would allow me to unlock, and I can only assume that the optical sensor is more easily thrown off by gunk on the screen, or my fingertips, or changes in temperature, or whatever other day-to-day stuff you shouldn't need to worry about when unlocking your phone.

Inscreen fingerprint

It's a hassle to use, and even when it works it's painfully slow. It's telling that Huawei provides two other (excellent) unlock methods in the Mate RS -- face unlock and a traditional fingerprint scanner on the back -- because using in-display fingerprint alone would be maddening.

Of course, the $2000 starting price of the Mate RS gives Huawei and Porsche Design plenty of wiggle room to include these extra components. The Mate RS itself is also something of a quirky device, not expected to sell in large numbers. I couldn't imagine Samsung wanting to shell out for an in-display fingerprint scanner and a backup capacitive option around the back, in a phone with traditional flagship pricing and expected sales numbering in the tens of millions.

Instead, every big-name flagship phone has made the (probably correct) decision to stick with the tried-and-true capacitive fingerprint technology while waiting for in-display tech to improve.

That said, it's also hard to avoid the conclusion that face unlocking in smartphones, even without a dedicated IR laser array like Apple's FaceID, is improving at a far quicker pace than in-display fingerprint. The former is here today in phones including the Mate RS, and works so well that I've basically ignored the in-screen fingerprint scanner throughout my entire time with the handset.

The demand for in-screen technologies is unlikely to wane anytime soon, but the stuff that's shipping today lacks the maturity required in such a core part of a modern smartphone. Give it a couple of years, and in the meantime appreciate the speed and accuracy of your current phone's fingerprint scanner.

What else is going on?

  • Oh right, it's Google I/O next week. Andrew has a great rundown of everything we're expecting to see in Mountain View from next Tuesday. Personally, I'm hoping for details on the future of Material Design, further revelations around Android P, and a clearer picture of where Wear OS is going.
  • I'd also love to hear something more concrete on Google's plan around the Fuchsia operating system. Eventually it'll need to bring developers into the loop on the next-gen OS, and I/O is as good a time as any to do that.
  • As good as the LG G7 ThinQ (you're welcome) is, I agree with Daniel Bader that it won't do much to get LG's mobile division out of its current rut. The company is treading water with another solid phone that probably won't move the needle. And rumors of an LG V35 this summer, presumably followed by a V40 in the fall, paint a schizophrenic picture of the company's late-2018 roadmap.
  • We're also not far off from OnePlus 6 launch season. And I agree that, with an anticipated price rise, the camera is the one thing that has to improve this year.
  • Just as important: Consumer trust. 2017 was a year of embarrassing blunders for OnePlus, ranging from the comical (send your phone in for a firmware update for HD Netflix) to serious (credit card data breach). Once the 6 is out in the wild, OnePlus needs the next 12 months to pass without any high-profile screw-ups.

That's it for now. See you at I/O next week!