How to Lock Your iPhone 4
Set up a passcode on your iPhone 4 to prevent people from accessing your device. Setting up a passcode lets you enable a timer that will automatically lock your iPhone if you leave it on and step away from it. Alternatively, the passcode will be required anytime after the iPhone is awakened from Sleep mode or turned on. Setting up a passcode so you can lock your device can be through the Settings app.
Tap the "Settings" app and then tap "General."
Tap "Passcode Lock" and then select "Turn Passcode On." Use the number pad that appears on the screen to tap in a 4-digit passcode and then re-enter your passcode to verify your passcode.
Tap "Require Passcode." Select a period of inactivity after which your iPhone will be locked and the passcode that will be required to access the device. Tap the "Passcode Lock" arrow in the upper-left corner of the screen to save your selection and return to the previous screen.
Tap the ON/OFF toggle to the right of Simple Passcode until "OFF" appears if you want a more complex passcode.
Enter your current passcode using the number pad that appears on the screen. Enter your complex passcode using the keyboard that appears on the screen and then tap "Next" in the upper-right corner of the screen. Re-enter your complex passcode to verify it.
Press the "Home" button at the bottom of the screen to save your changes and exit the Passcode Lock screen and return to the iPhone home screen.
Press the "Sleep/Wake" button along the upper-right edge of your iPhone at any turn to put the iPhone screen to sleep. Immediately after waking the iPhone up you will need to enter your passcode to access the device.
Tips & Warnings
- If you forget your passcode, you will need to format your iPhone 4 and restore it from a backup.