I am not a native English speaker so I need a little help to find the right name of the component that I am looking for. I have a device that has a touch panel with 3 touch buttons. They are capacitive touch buttons (cannot be pressed). Below the glass panel (actually it is plastics) there is something that looks like a graphite sponge and below the graphite sponge there is a kind of tactile button which is not a mechanical button but I guess captive (it is flat, cannot be pushed). 4 pins. Other cheaper versions of the device, has the same PCB but has physical tactile buttons soldered instead of this capacitive buttons.
You're probably right...
It's very likely a capacitive keyswitch body. The 4 pins are DC power (2x) and a floating output (typically the collector and emitter of an NPN). The sponge (which isn't graphite) conducts the electric field lines down to the electrode (plate) in the well of keyswitch body.
This particular part must be old or custom as I couldn't find anything like it in that formfactor. The closest ones I found are configured like this:
Maybe someone else will have better luck?