The next iPhone has long been rumored to have an all-glass front in its 2017 revision, with the Home button and Touch ID sensor being built into the display itself. The solid state Home button in the iPhone 7 is more than likely a half-step leading in that direction.
Chinese brand Xiaomi has launched new phones today that actually use a built-in fingerprint sensor, so the technology is available and is being used in the real world. The mi 5s and mi 5s Plus both have an ultrasonic fingerprint reader that is built right into the glass.
Not only does ultrasonic imaging allow for the reader to sit beneath the glass, but it is also more accurate than capacitive sensors such as Touch ID. With Xiaomi’s implementation, they’ve put an indent in the glass to help users locate the sensor, something that’s been seen in early iPhone mockups.
It’s worth noting that Xiaomi’s implementation has the reader beneath the glass, but on top of the actual display, meaning all the home screen icons are above the fingerprint reader. So the front is all-glass, but the display doesn’t over the entire front.
Unfortunately, the entire video is in Chinese so we’re showing the sensor in use.
As seen, this approach is what we’ve seen in this mockup. Though, it does show that the display is extended into the fingerprint reader itself.
It’s more likely that Apple will build the sensor into the entire display so it wouldn’t matter where you touched it as the display itself will act as the sensor. Doing such a task may be fairly difficult, however.