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.
There is a conductive pad on the bottom side of the button that "shorts" out the spiral. Usually dark grey since it is carbon based.
The spiral just give you a higher probability that the pad will touch both sides at the same time.
The spirals are electrical contacts. Shorting the traces in a spiral causes the keypress to be detected.
The backs of the keys have a layer of conductive rubber or plastic. Pressing that layer against the spirals closes the circuit just like you had use a piece of wire to make the connection.
The black rubber on the back of the keys is actually somewhat conductive and provdes a current path between these swirls once a key is pressed.
