Rumor has it Apple is planning to release an all-screen iPhone in 2017 with a button-less Touch ID scanner built right into the display. Now a newly published patent may reveal one way the company could pull it off.

The patent, which was published this week and filed back in 2015, describes a pretty straightforward “Man-machine interface” that uses some sort of biometric sensor for authentication. Apple actually lists three different types of fingerprint reader technology. There’s optical, capacitive (currently used for Touch ID) and ultrasound imaging, which could put the sensor underneath a glass display.

The patent notes that ultrasound imaging is the “most accurate but least common” option. Here’s how the technology works according to Apple:

In this type of sensor, two transducers are placed on the x- and y-axes of a plate of glass–one each for receiving and transmitting–for propagating ultrasound waves through a glass plate; when the finger is placed on top of the glass, the finger impedes the waves and the receiving transducer can measure the alteration in wave patterns.

If Apple decides to adopt this technology, it would mean hiding the Touch ID scanner behind a glass surface, potentially making it possible to expand the display all the way down to the phone’s bottom edges. The company’s already secured a couple of other patents focused on removing bezels from future devices, suggesting it’s serious about this new design.

There’s no guarantee Apple will actually go through with any of these patented ideas, but if the company really is planning a bezel-free iPhone for 2017 this could be the way to make it happen. If it doesn’t use its own tech, it could always adopt something similar from LG.