Touch screens

The two most commonly used systems are resistive and capacitive touch screens.

These are the most basic and common touch screens, the ones used at ATMs and supermarkets, that require an electronic signature with that small grey pen. These screens literally “resist” your touch; if you press hard enough you can feel the screen bend slightly. This is what makes resistive screens work – two electrically conductive layers bending to touch one another, as in this picture:
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Resistive

One of those thin yellow layers is resistive and the other is conductive, separated by a gap of tiny dots called spacers to keep the two layers apart until you touch it. (A thin, scratch-resistant blue layer on top completes the package.) An electrical current runs through those yellow layers at all times, but when your finger hits the screen the two are pressed together and the electrical current changes at the point of contact.

capacitive

Unlike resistive touch screens, capacitive screens do not use the pressure of your finger to create a change in the flow of electricity. Instead, they work with anything that holds an electrical charge – including human skin. Capacitive touch screens are constructed from materials like copper that stores electrical charges in an electrostatic grid of tiny wires, each smaller than a human hair.