The first touchscreen ever invented was CERN’s SPS Control System that had a display with buttons which could be touched. The display would show tree, branches and leaves in order to help the operator run the entire facility with only a couple of touches.
The touchscreen was developed at CERN in 1977 by Bent Stumpe, a Danish electronics engineer, for the control room of CERN’s accelerator, the SPS (Super Proton Synchrotron).
A lot of details can be read in the video description from here:
Modern touchscreen technology, as used in smart phones and tablets, still uses the fundamental design principle of the capacitive touchscreen panel developed at CERN. Modern touchscreens consist of an insulator such as glass, coated with a transparent conductor such as indium tin oxide (ITO).
As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen’s electrostatic field, measurable as a change in capacitance. Different technologies may be used to determine the location of the touch. The location is then sent to the controller for processing.
So whenever anyone asks “what has CERN done for the world?”, along with the World Wide Web, all the modern smartphone and tablet touchscreen technology started there too, proving once again that science is an engine of prosperity and that the technology being formed there now may very well end up in your pocket a few decades down the line with an entire industry invented behind it.