One of the iPhone's most advanced internal technologies is its accelerometer, which allows it to detect three-dimensional motion and translate it into movements on the screen. This means that when you tilt the phone, the screen should move as well. If your screen does not tilt, one of several glitches may be occurring.
An accelerometer is a mechanical device that measures shifts in forces, or acceleration. While you may think of acceleration as a car speeding up, this is not the only way acceleration manifests. In fact, gravity is a form of acceleration, and this is the force that the accelerometer typically measures. By detecting shifts in gravity using tiny, weight-loaded springs, the accelerometer can tell where the phone has been moved. These springs form three axes, so they can detect shifts from side to side, forward to backward and up and down – all three dimensions.
Several applications from the iTunes App Store can help you determine if your accelerometer is functioning properly. Sometimes, the accelerometer itself may be broken; in this case, you will need to replace the phone. Often, though, a certain app or piece of iPhone software may be misreading the accelerometer data. To see if a certain program is the culprit, try tilting and shaking the iPhone with different programs open, such as Safari, Compass, Labyrinth, Instapaper, iFishing or Urban Spoon.
If you discover that only one of your applications malfunctions with the accelerometer, you may need to update that app. Tap the App Store icon on your iPhone's home screen, and tap "Updates" to see if that app needs an update. If you experience glitches in several apps, you may need to update your iPhone's operating system. Connect it to your computer, open iTunes, click on your iPhone's name under "Devices" and click "Check for Updates" in the center screen. If many users discover a problem, Apple will release a fix in a software update, and you will be able to download it from iTunes. Also, make sure that your iPhone's screen is not locked in portrait mode. Double-tap the Home button and swipe the screen from left to right. Tap the button that looks like an arrow making a circle if it shows a padlock in the center.
Sometimes the iPhone simply needs to reboot. If you find you are having a sudden problem with the accelerometer, try resetting the iPhone by holding down the "Sleep/Wake" button (on the top of the device) and the "Home" button at the same time for about 10 seconds, or until the Apple logo appears. If this does not fix the problem, try restoring the device. Connect it to your computer, open iTunes, click your iPhone's name under "Devices" and click "Restore" in the center screen. If this still does not fix the problem, your accelerometer is probably faulty. Take the device to your local Apple Store and let a Genius support member examine it. If the phone is under warranty, you may get a replacement.