I am no posek either, but for an examination of some of the issues involved please see the Star-k website, and particularly the lecture regarding "Sabbath mode" ovens. For instance, while the Chazon Ish ruled that completing a circuit may be "boneh" [completing] in an electronic device there may be no visible physical change as the switching is taking place within the electronics. Also, modulating a current may be less of a problem as you are not completing a circuit. In that regard a touch screen may be less problematic than a keyboard. Causing the voice device, or another device which it controls, to respond by your voice commands is another issue. None of this is cut and dried and there are differing opinions. There are technologically savvy Rabbis to ask.