Why There’s No Fingerprint Sensor on the iPhone XS

Woman holding a iPhone XS, using Face ID.
Photo illustration by Slate. Photos by Apple and Alexa Suter on Unsplash.

Before the iPhone XS and XS Max made their debut earlier this month, many Apple watchers had wondered whether the company would adopt an emerging technology that enables fingerprint sensing without a home button. Apple switched from a hardware home button that physically depresses to a touch- and fingerprint-sensitive alternative in the iPhone 7. With the iPhone X last year, Apple removed the home button—and Touch ID—altogether in favor of swiping-based gestures and facial recognition (Face ID). The question remained, however, whether Apple would permanently eliminate fingerprint sensing as an authentication method, or whether its absence in the iPhone X was merely a pause until Apple adopted the latest technology.

In-screen fingerprint sensing is an engineering feat that involves embedding fingerprint-detecting sensors beneath the surface of a device’s display. It’s typically an optical system, relying on LEDs and light-sensing diodes for authenticating a fingerprint rather than using capacitive sensors, the kind typically used in button-based fingerprint detectors. Optical fingerprint technology historically hasn’t been ideal for smartphone use because it’s thicker than capacitive alternatives. However, it’s the type often used in stand-alone fingerprint sensors and in larger electronics, such as laptops.

The technology has finally been slimmed enough to be feasible in smartphones, and new manufacturing methods have been developed that would allow it to work from underneath a phone’s display. Rumors started by a patent filing published in early 2017 suggested that Apple could include the technology in the new iPhone that year. When that didn’t pan out with the iPhone X, reports recirculated this year until a research note from a prominent Apple analyst dispelled that idea. Apple then announced its new phones—sans fingerprint sensors—once again. While Apple has intellectual property around in-display fingerprint sensing, it isn’t rushing the technology into its devices just yet.

Instead, a small number of Android manufacturers who’ve already begun adopting in-display fingerprint technology into their upcoming phones will be the guinea pigs. OnePlus confirmed that its OnePlus 6T smartphone will have an in-display fingerprint reader—and will likely be among the first phones available in the U.S. with one when it debuts (likely in November). The recently announced Xiaomi Mi 8 Pro has fingerprint-sensing technology built into the display, along with facial recognition in its front-facing camera. Other phones such as the Vivo V11 and Huawei Mate RS also include in-screen fingerprint sensors, but they’re not yet on sale in the U.S.

Facial recognition and fingerprint detection both have their benefits and drawbacks as security measures. According to OnePlus, in-screen fingerprint detection “reduces the number of steps to complete the action” of unlocking a phone. Instead of needing to pick up a phone and position it in front of your face, you need only press your finger on the display. However, optical fingerprint detectors may be less secure than facial recognition or other fingerprint detection methods. They can be more easily fooled than other biometric authentication methods because they only validate a 2D image of an individual’s print. Facial recognition, meanwhile, has proven frustrating for users trying to unlock their phone first thing in the morning. It can also be tricked with high-quality 3D-printed masks made of stone powder (reminiscent of Mission Impossible).

It’s possible Apple will never opt for an in-display fingerprint sensor. It’s unlikely Apple would include such a solution if it weren’t at least as secure as Face ID. However, there are alternatives that could make it more secure. Ultrasonic-scanning technology, which captures 3D fingerprint data via an ultrasonic pulse, could be used underneath a phone’s display instead of or in addition to an optical solution. For now, however, consumers are largely satisfied with Face ID, and in-display fingerprint sensing is a commercially untested technology. Android device owners will get to try it out and discover any pitfalls. If reaction is positive, it could be an option for iPhone users soon—maybe even as early as next year.