Hi all Thanks for the replies, I looked at the cover and the small square magnet is there and a quick pass over with some iron shows that the magnet is in fact quite magnetic! I looked at the spot on on the board that lines up with the magnet and it seems like the magnet fits into the small rectangular gap between the slide switch for the internal card and the battery. In there is a small yellow component on the board that might be a reed switch [?] that looks to be intact and connected.