OnePlus 6T will be the first real test for in-display fingerprint sensors

It's official: The OnePlus 6T will have an in-screen fingerprint scanner.

The news comes via CNET, which confirmed the rumor with OnePlus. "By adding this feature as an addition to other display-unlocking options such as Face Unlock, users will have options to unlock the display in a way that is most efficient for them," the company told CNET.

And even though the OnePlus 6T won't be the first phone with this feature, it will be the most important test for in-display scanners so far.

In-display fingerprint scanners differ from typical, capacitive fingerprint scanners as they're placed under the smartphone display instead of somewhere on the phone's chassis. They can be optical or ultrasonic; an optical sensor, as seen on some phones from Chinese brand Vivo, illuminates your fingertip as you press the screen and captures the reflection, then compares that to the image it got when you registered the fingerprint. They should be roughly as secure as capacitive fingerprint scanners (such as the iPhone 8's), but are a little tougher to get to work in practice. This is mainly because the display -- semi-transparent as it may be -- is still in the way, between your finger and the sensor.

I've tested two phones that feature an in-display fingerprint sensor: Vivo X21 and the Vivo NEX S, and had hands-on time with several others. The bad news is that none of them worked flawlessly. At worst, they were unusable, forcing me to delete my fingerprint and register it again. At best, I was able to register a fingerprint and unlock the phone with it sort of reliably — maybe 80 percent of the time. And still, there would come a bad streak, often at the worst possible time, during which I wasn't able to unlock the phone with a fingerprint at all, forcing me to enter my PIN or password.

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I suspect I'm not the only one with such issues, but you probably haven't heard much about them because none of the phones with in-display fingerprint scanners have so far been available in North America, with limited exposure to Europe. Had Samsung or (heaven forbid) Apple launched a phone with a fingerprint scanner that performed like this, you'd never hear the end of it.

Paving the road for Samsung?

The OnePlus 6T will be different. The OnePlus brand is well-known in the U.S. and Europe, and has been lauded by numerous reviewers for making great and yet affordable phones. The OnePlus 6T is the company's next flagship, and for many users in Europe and the U.S. it will be the first encounter with in-display fingerprint-scanning tech.

It's impossible to say in advance how well OnePlus 6T's fingerprint scanner will perform. OnePlus' parent company is the Chinese electronics giant Oppo, so it's safe to assume that the tech will be an evolutionary upgrade of (or the same thing as) the in-display scanner found in Oppo's R17 Pro, which I haven't tested. I do have to say that none of the in-display fingerprint scanners I did try have been anywhere near perfect.

OnePlus is aware of this peril. The company told CNET that the technology "wasn't mature enough" to include on a OnePlus phone -- until now.

We won't know for sure until we can test the OnePlus 6T ourselves, but the way its in-display fingerprint scanner performs will have implications for other brands' phones as well. Rumors say Samsung has been trying to introduce this technology to its phones for years, but it keeps getting delayed as it's not quite there yet.

The OnePlus 6T won't live or die by the quality of its fingerprint sensor. The phone will also have face-unlocking technology, which greatly offsets issues with the fingerprint reader — I've relied on it a lot on the aforementioned Vivo phones, and after a while I turned off the fingerprint scanner completely. But if OnePlus manages to polish it to make it at least nearly as good as traditional fingerprint scanners, it might (finally) usher an era in which this technology becomes commonplace.