Inventor/madman Dominic Wilcox created the Finger-Nose stylus specifically for use in the bath. It's basically a plaster nose with a capacitive stylus embedded inside, protruding slightly from the tip of the plaster. (You can't just use the plaster itself; capacitive touchscreens, used in just about every modern smartphone, rely on an electrical charge from either naked human skin or specially-designed styli.) Curiously, the plaster he used has embedded fibers to make it look slightly hairy, though there are still several steps he would need to take before anyone believes this giant white nose with highly visible face-straps is an organic part of one's face.