1. Interact with S4 with a twitch of your eyeballSmart Stay is probably one of hottest features of Samsung Galaxy S4. With Smart Stay enabled, the phone detects your eyes by the front camera and as long as you are looking at the screen, your phone screen will not be darkened. Thus, you can also scroll up and down Web pages simply by tilting your head, and videos will pause when you turn your face away from the display.
To enable it Go to Settings > My Device > Smart Screen.