As we continue to explore the Voyage, we come across the PagePress sensors. The sensors are held to the display assembly with some mild adhesive for good contact.

"PagePress is a custom-designed force sensor made of carbon and silver, which reacts to a subtle increase of pressure, triggers a page-turn, and provides a haptic response only your thumb can perceive."

Sounds like some kind of strain gauge implementation to us. A strain gauge is a component that changes resistivity when deformed, making for an excellent buttonless button.