Judging from old reviews of the phone, it looks like a positional proximity sensor. The screen had a blue hover glow where your finger approached the screen.

It was literally a screen mounted on a button, actually.

The whole screen was mounted on a big button, so touching it was hovering and you'd press the screen with a satisfying click to execute something. It wasn't the most reliable if you weren't careful, but why not do that with a pressure sensor nowdays?

Also known as force touch on an iPhone.

I've not used an iPhone for a while, but according to Google search:

> The iPhone 11 and iPhone 11 Pro will ditch 3D Touch in favor of "Haptic Touch," according to Apple's website. ... The new iPhones' Haptic Touch will be responsive to how long users hold down, but not the force of the tap.

I would love that feature, but I think it has to be very integrated into the software and the APIs of the phone OS or no one will actually use it.

I loved force touch but it's gone now. On MacOS the touchpad still has force touch, and hard pressing on a word anywhere in the OS brings up dictionary definitions. It's amazing for language learners.