The screen resolutions of the first three iPhone models are 320 x 480 (HVGA) at 163 ppi, and 640 x 960 at 326 ppi for the iPhone 4. The touch and gesture features of the iPhone were originally developed for Apple by FingerWorks. Most gloves and styluses are incompatible with the iPhone because they are not able to generate the necessary electrical conductivity, but there are capacitive gloves and styluses that work on the iPhone's touchscreen. The iPhone 3GS also presents an oleophobic coat that prevents fingerprints.
The iPhone presents a minimal hardware user interface, holding only four or five buttons, depending on whether the volume keys count as one, or two separate buttons. On the iPhone 4, they are two separate, circular buttons, one for increasing and one for decreasing volume. On all other iPhone models, both buttons are located under the same plastic panel, known as a rocker switch. In both cases, the volume keys are located on the left spine of the device. The only menu button available is the Home button. It is called so because pressing it automatically leads to closing the current application and redirecting the user to the home screen(from where applications are selected).
This button is situated right under the screen. The iPhone's power button is located on top of the device, and it is called the Awake/Sleep button. Although its main role is to turn the device on or off, it can also perform secondary tasks. When it is pressed during a call, it turns the phone's mode to "silent", while pressing it twice send the call to voice mail. There is another button on the phone's spine, which turns it to mute, and eliminates all sound. Apple implemented three sensors to which the iPhone responds.
The proximity sensor deactivates the display and touchscreen while the phone is brought near the face. This is done both to save battery and to prevent inadvertent content from being close to the user's face and ears. A light sensor helps the phone automatically adjust the display's brightness. This helps save battery as well. The first sensor is a 3-axis accelerometer sensor which helps the iPhone orientate, and identify if it goes right, left, up, down, or it performs any other movements, so it makes it very easy for users to switch between portrait mode and landscape mode.