Capacitive Technology

• Prior to the iPhone, most touchscreens were pressure-sensitive and detected contact when two conductive films were pushed together by a stylus. The iPhone uses a different technology called a capacitive touchscreen. This technology detects contact by placing a transparent film beneath the glass front that acts as one side of a capacitor. Your finger acts as the other side of the capacitor, and a small electrical current is detected by the iPhone wherever your finger makes contact with the screen.
  
  

Multi-touch & Gestures

• Capacitive touchscreen technology has the added benefit of being able to detect multiple points of simultaneous contact at any one time, whereas pressure-sensitive touchscreens can only detect one point of contact. The iPhone's multi-touch touchscreen allows you to use gesture commands to controls the device and its applications, such as pinching two fingers together to zoom in, or tapping or swiping with two or more fingers to perform a different on-screen action than a one-finger tap.
  
  

Input Detection

• Capacitive touchscreens can detect only contact by a conductive material, with the skin on your finger being a prime example. This limits the accuracy of detection for actions such as writing on the screen, as a traditional pen-shaped stylus does not work on the iPhone's touchscreen. Styli are available that mimic the bio-electrical reaction of your finger against the capacitive touchscreen detector, though the large rubberized tip generally doesn't offer any more accuracy than a fingertip.
  
  

Viewing

• The iPhone features a color, back-lit LCD screen as part of the touchscreen's construction, which displays the images you interact with when touching the device. The LCD is positioned directly beneath the touchscreen detector to give the impression of interacting directly with the image. The back light has an adjustable brightness to help you see the image in extremes of bright light and darkness. A light detector is present on the iPhone's front casing to automatically adjust the touchscreen's brightness when the ambient light level changes.