Hall Effect Switch Keyboard
Hall Effect Switch is a high quality and expensive to manufacture switch used in the 1980s mostly. It is used by lisp machine keyboards. 〔➤see Space-cadet, Lisp Machine Keyboards〕
Hall effect keyboards use a solid state sensor (in a microchip found inside each switch) to detect the movement of a magnet by the potential difference (voltage) that the magnet creates across a wire. A typical implementation of a Hall effect switch consists of a linear switch which has a magnet attached to the end of key slider, whose movement when the key is pressed actuates the switch. They are extraordinarily reliable, with an expected lifetime measured in billions of key presses. However, they are too expensive for general use, and are usually reserved for military and aerospace applications.
[2016-11-12 from https://deskthority.net/wiki/Contact_mechanism#Hall_effect]
Someone made a keyboard using the Hall Effect switch. Available for purchase on massdrop at https://www.massdrop.com/buy/xmit-hall-effect-mechanical-keyboard?mode=guest_open