iPhone 4S has a feature that auto locks when iPhone is unused after certain period of time. The default value for auto lock time period is set to 1 minute. iPhone 4S users can choose option ranging from 1 minute to 5 minutes and or they can completely disable this feature.
Step 1:- Press the menu button on iPhone.
Step 2:- Tap the settings icon on the Home screen.
Step 3:- In the Settings screen, scroll down to Auto-Lock option.
Step 4: – Tapping on Auto-Lock option would display the different values available for Auto-Lock. Now select Never from the available list. This would turn off the Auto-Lock feature on iPhone 4S.