The touchscreen on all models is a 9 cm (3.5 in) liquid crystal display with scratch-resistant glass.[41] The capacitive touchscreen is designed for a bare finger, or multiple fingers for multi-touch sensing. The screens on the first three generations have a resolution of 320 × 480 (HVGA) at 163 ppi, while that of iPhone 4 and iPhone 4S has a resolution of 640 × 960 at 326 ppi.
The touch and gesture features of the iPhone are based on technology originally developed by FingerWorks.[42] Most gloves and styluses prevent the necessary electrical conductivity;[43][44][45][46] however, capacitive styli can be used with iPhone's finger-touch screen. The iPhone 3GS and later also feature a fingerprint-resistant oleophobic coating.[47]
The top and side of an iPhone 3GS, externally identical to the iPhone 3G. From left to right, sides: wake/sleep button, SIM card slot, headphone jack, silence switch, volume controls. The switches were black plastic on the original iPhone. Top: earpiece, screen.
The iPhone has a minimal hardware user interface, featuring only four or five buttons, depending on the generation. The only physical menu button is situated directly below the display, and is called the "Home button" because it closes the active app and navigates to the home screen of the interface. The home button is denoted not by a house, as on many other similar devices, but a rounded square, reminiscent of the shape of icons on the home screen.
A multifunction sleep/wake button is located on the top of the device. It serves as the unit's power button, and also controls phone calls. When a call is received, pressing the sleep/wake button once silences the ringtone, and when pressed twice transfers the call to voicemail. Situated on the left spine are the volume adjustment controls. The iPhone 4 has two separate circular buttons to increase and decrease the volume; all earlier models house two switches under a single plastic panel, known as a rocker switch, which could reasonably be counted as either one or two buttons.
Directly above the volume controls is a ring/silent switch that when engaged mutes telephone ringing, alert sounds from new & sent emails, text messages, and other push notifications, camera shutter sounds, Voice Memo sound effects, phone lock/unlock sounds, keyboard clicks, and spoken autocorrections. This switch does not mute alarm sounds from the Clock application, and in some countries or regions it will not mute the camera shutter or Voice Memo sound effects.[48] All buttons except Home were made of plastic on the original iPhone and metal on all later models. The touchscreen furnishes the remainder of the user interface.
The display responds to three sensors (four on the iPhone 4). A proximity sensor deactivates the display and touchscreen when the device is brought near the face during a call. This is done to save battery power and to prevent inadvertent inputs from the user's face and ears. An ambient light sensor adjusts the display brightness which in turn saves battery power. A 3-axis accelerometer senses the orientation of the phone and changes the screen accordingly, allowing the user to easily switch between portrait and landscape mode.[49] Photo browsing, web browsing, and music playing support both upright and left or right widescreen orientations.[50]
Unlike the iPad, the iPhone does not rotate the screen when turned upside-down, with the Home button above the screen, unless the running program has been specifically designed to do so. The 3.0 update added landscape support for still other applications, such as email, and introduced shaking the unit as a form of input.[51][52] The accelerometer can also be used to control third-party apps, notably games. The iPhone 4 also includes a gyroscopic sensor, enhancing its perception of how it is moved.
A software update in January 2008[53] allowed the first-generation iPhone to use cell tower and Wi-Fi network locations trilateration,[54] despite lacking GPS hardware. The iPhone 3G, 3GS and 4 employ A-GPS, and the iPhone 3GS and 4 also have a digital compass.[55] iPhone 4S supports GLONASS global positioning system in addition to GPS.