How do touch screens work?

Touch screen technology prior to the iPhone used the “resistive” method. The idea behind the “resistive” method is quite simple: two thin layers, usually made of tough plastic, are spaced a minuscule distance apart with electricity running in between. The screen is above the upper layer and the LCD display is below the bottom layer. When the screen is pressed, it forces the top layer against the bottom layer so sensors can detect where the two meet. One of the best conveniences of this method is that it can detect touch from anything that presses down on the layers, whether it is a finger or a pen cap. However, this method can only recognize one point of contact because only one point can be fully depressed at a time and as a result, does not have smooth sliding and dragging motions (“Touch screens”). Although this method is now considered largely outdated due to the mass market of iPhone technologies, it is still used on some ATM s and in-car screens.