The Zomet Institute has designed the “Shabbatphone” for those engaged in vital (non-life saving*) services on Shabbat. It works on the principle of changing electric capacitance. Numbers are printed on a smooth sealed surface. On ordinary phones, pressing buttons completes electric circuits, which Jewish law prohibits on the Sabbath. (*Jews may of course break Shabbat laws in order to save life.)
http://www.timesofisrael.com/new-smart-shabbatphone-is-kosher-even-on-the-weekend/