Touchscreens work by detecting the presence and location of a touch within the display area. There are several technologies used to do this, including resistive, capacitive, and infrared.
In a resistive touchscreen, the screen is made of two layers of material separated by a small gap. When an object, such as a finger, presses down on the screen, the two layers come into contact, and the location of the touch is detected by sensors on the edges of the screen.
In a capacitive touchscreen, the screen is coated with a material that can store electrical charge. When a finger touches the screen, it changes the amount of charge stored at that point on the screen, and the location of the touch is detected by sensors on the edges of the screen.
In an infrared (IR) touchscreen, the screen is lined with infrared light-emitting diodes (LEDs) and photodetectors that form a grid of infrared light beams across the screen. When an object, such as a finger, touches the screen, it blocks some of the beams, and the location of the touch is detected by the photodetectors.
Both resistive and capacitive technologies require the touch of skin or special stylus to work, as they detect changes in electrical properties on the surface of the screen. IR touchscreens can work with gloved hands and can be useful in tough or hostile work environments.