im not sure which design you have, some are three layers of plastic the
middle one containing holes when key pushed it makes the outer two layers
connect, what i think you have is the type that is in alot of things these
days.
my only knowledge of hall effect is in automobiles and if im right i think
there is a sensor that picks up on the magnetism, but yours i think has
the interwoven copper tracings on the board/film and the little rubber pad
has some sort of black disk underneath it, when the disk touches the
coppertracings it completes the circut, how it works im not sure, but
there is no processor needed to detect the signal, you could feed an led
lamp of off it and it would receive a weakend current through it, maybe
that pad is some sort of conductor