You can also view previously answered questions in the HSW Question Archive . They certainly have advantages, and the most important is the fact that dirt and moisture cannot get into the switch to gum it up or damage it. Temperature - The human body is generally warmer than the surrounding air.
Many elevators therefore use buttons that are sensitive to the warmth of the human finger.
These buttons, of course, don't work if you have cold hands. They also have the unfortunate property of taking an elevator to a floor where a fire is burning. The motion-sensitive lamps you see on people's patios also sense the heat of the human body. Resistance - The human body, being made mostly of water, conducts electricity fairly well. By placing two contacts very close together, your finger can close the circuit when you touch it.