“Make the most of that beauty spot. Ultrathin temporary electronic tattoos can now turn body blemishes into touch-sensitive buttons, letting you control your smartphone with your own wrinkles, freckles and other skin features. People intuitively know the location of their own bumps and birthmarks, which makes them ideal locations for touch-sensitive buttons, says Martin Weigel at Saarland University in Saarbrücken, Germany, who has led the research. You could squeeze a freckle to answer a phone call, or slide a finger over your knuckles to change the volume of your music. Weigel and his colleagues at Saarland University and Google used conductive ink to print wires and electrodes on temporary tattoo paper. The tattoos, which they call SkinMarks, are thinner than the width of a human hair. They are transferred onto the skin using water and last a couple of days before rubbing off.”