If companies want to thrive, they need to understand want customers want, create products to answer that demand, observe the competition, and keeping up with the trend.
The same goes for smartphone manufacturers.
Phones were once half numerical pad with the rest lesser part as screen. When communication in form of texting became more common, the traditional numerical pads were replaced by small keyboards. Then after the internet became popular on mobile, streaming media, and powerful cameras have been adopted, larger screens with touch capabilities were supported.
And when smartphones became larger and larger from people demanding better mobile experience, they eventually realized that big phones are simply too big for one-hand usage. This created the demand for smaller phones.
So how to accommodate big screens on smaller phones? The answer is by creating thinner and thinner bezels. But this again created a drawback: where can manufacturers put their front-facing camera? Some opted for popup cameras, while some use in-screen cameras.
And how about the fingerprint scanner? Some opt to put it on the back, on the side, and eventually, underneath the screen.
This is called in-screen fingerprint scanner. So, how does it work?
Over the decades of smartphone usage, the earliest security measure to prevent unwanted access is by using passcodes. This was later improvised for usability experience using patterns, iris scanner, to fingerprint scanners and facial recognition.
But the method most widely-accepted, based on popularity and convenience, is by using the fingerprint scanner.
As smartphones evolve, screens have occupied most of the front-facing part of the devices. Because the easiest way to use a fingerprint scanner is by using a thumb, the most obvious way for manufacturer to meet both a no bezel screen with security, is to use this in-screen fingerprint scanner.
Essentially, the technology involves hiding the sensor for the unlocking mechanism under the display.
There are basically two types of in-screen fingerprint scanner:
Optical Sensor
This method is the older of the two.
Simply put, it uses an optical in-screen fingerprint scanner which works by projecting light.
Here, the functioning area of the in-screen scanner illuminates the finger. After that, a sensor or camera placed underneath the screen grabs the reflected image of the digit. The algorithm then comes to play by comparing the image with the stored version of the fingerprint.
if it matches, the device unlocks.
Ultrasonic Sensor
While optical is an older technology, the newer ultrasonic approach is taking things another step forward.
This method uses ultrasonic instead of light. It works by first generating high-frequency sound waves which interacts with the finger's skin. Another sensor placed underneath the display, reads the information that bounces back.
Ultrasonic is capable of generating a 3D map of a digit, making it capable of capturing the ridges and pores better than that on flat image of the optical approach. As a result, this sensor can work even when the users' finger is dirty or wet.
Ultrasonic sensors are more expensive to create than the optical ones, but they have the potential of being faster and more secure thanks to the additional data they capture.
Ultrasonic is also seen as a more reliable approach, because the optical method uses light source that can degrade over time, similar to a photocopy machine.
This method is also regarded as a better technology because it can still operate through thin opaque materials such as glass, aluminum, plastic, sapphire or even steel. Therefore, the scanner can be embedded under the display or even under the display, allowing for a more discrete look and thinner bezels.
In terms of security, both methods should be as secured as when using physical fingerprint scanner.
However, the optical sensor which maps 2D image of a finger is deemed less secured than its ultrasonic counterpart. In theory, people might be able to fool an optical sensor with a photograph of a fingerprint, an ultrasonic in-screen scanner is much harder to fool, as they may need a 3D model of a finger.
Even that might not work depending on the technology.
In terms of speed, in-screen sensors can be slower than the physical scanners. And they can also be less reliable due to the fact that the signal (light or ultrasonic) needs to pass through solid medium which can be contaminated with dust and scratches, lowering their accuracy.
And can be worse if users put screen protectors on their devices.
In general, in-screen fingerprint scanner is more than just a gimmick. It's the answer by phone manufacturers that want meet the demands of a truly fullscreen display, without having a byproduct the industry called 'notches', like the ones originally 'created' by Apple with its Face ID.
But when it comes to practice, the trade-offs compared to traditional physical fingerprint scanners include: thicker and heavier phones, and a more expensive device.
What's more, in-screen fingerprint scanners don't introduce or improve the traditional physical scanners.
And there is also the fact that different manufacturers put their sensors differently. The inconsistent placement is rather less intuitive in practice. But this is just a matter of habit; users get used to it wherever it is. There really isn't some abstract, natural experience of unity with your phone's security that comes with poking the screen rather than the back or bezel.
Related: Under-The-Screen Smartphone Camera: How To Make An Opaque Object Transparent