The Mate 20 ProOnePlus 6T and Xiaomi Mi 8 Pro all feature an in-display fingerprint reader. But how do they work, and how will the tech evolve over the coming months?

Although the iPhone has moved to Face ID and others have experimented with facial and iris recognition, it seems that many of the big Android phones of the next year will stick with fingerprint ID as the main biometric entry point to your phone – even if they also hedge their bets in terms of supporting improved facial recognition as well.

Huawei’s in-display fingerprint sensor features on the new Mate 20 Pro and sister Honor Magic 2 phone following up on its previous patchy integration within the Mate RS (see below). Huawei wasn't the first manufacturer to plump for an in-display fingerprint reader though - see Vivo’s Nex S.

Optical vs ultrasonic

The scanners we've seen so far are optical scanners – these use some light to illuminate your finger. A tiny camera under the screen takes an image of your finger which is then compared to the stored image. 

Under-display fingerprint scanners can also be ultrasonic instead of optical – these more expensive units work using ultrasound to build up an image of your fingerprint (yes, really).

We believe an in-display fingerprint scanner will feature in Samsung’s Galaxy S10 and that this may be ultrasonic. That phone is due in early 2019.

According to leaks, that scanner could be a third-generation version of Qualcomm’s existing ultrasonic scanner which was first shown off in 2015 under the moniker of Snapdragon Sense ID.

We may hear more details about this scanner at Qualcomm’s annual Tech Summit which we’ll attend in early December.

Ultrasonic fingerprint readers are more accurate than their optical counterparts and therefore more secure.

For the second generation of sensors, Qualcomm talked about how it had improved accuracy, being able to scan contaminated fingerprints (for example, where water or sun cream is on the skin).

Current ultrasonics can penetrate through glass (up to 800 µm or microns thick) and metal (up to 400 µm), so expect a later generation to be able to work through thicker materials.

Qualcomm isn't the only name in fingerprint sensors though; Synaptics is another and their tech is behind Xiaomi's fingerprint sensor in the Mi 8 Pro (called Clear ID by Synaptics) as well as the previously-mentioned Vivo handset. 

Synaptics is a company that's been involved in computing and phone interfaces for more than 30 years; it developed the first computer touchpad and the touch tech for the click wheel on the iPod. Its tech is also used for many standard external fingerprint sensors on phones. 

More about the latest fingerprint readers

We do know that Huawei said its fingerprint reader features 10 level dynamic pressure sensing (dps) for improved accuracy. The Chinese handset maker says this can improve the unlock speed by up to 30 percent compared with the Mate 10 but it didn’t make any claims for improved accuracy.

In our Mate 20 Pro initial review, our reviews editor Mike Lowe calls it the best fingerprint reader of its kind – it’s responsive and accurate. One thing that we did notice was that it takes a while to set up the in-display fingerprint reader; that’s because you need to enable it to read your fingerprint thoroughly to improve accuracy.

We’d previously used the reader on the Porsche Design Mate RS equivalent and our experience with that reader wasn’t that great since it didn’t work for each possible instance. That’s not the case with the Mate 20 Pro.

We've used the OnePlus 6T fingerprint reader and, as with the Huawei version, the setup feels a little involved as you need to enable the sensor to capture a lot of detail. But once done the experience is beautifully responsive - almost as much as a physical fingerprint reader. 

OnePlus told us: "The particular coloured light chosen has been tested and deemed the best for accuracy and the durability of the tech used has passed 300 thousand taps and has shown no sign of deterioration"