I disassembled some old telephone and mobile phone. Every keypad is different, and yet, all of them have those "spirals" (see the image below) under the button or something similar.
What I don't understand is how those "spirals" can put in contact two ends of a wire. Are they some kind of sensor?
The two ends of a spiral are not connected. My guess is that when the button is pressed, they are short-circuited; however, I don't see how it should happen.