The auto-lock feature can turn the screen off while you are not using Surface. Many tablet are set to auto-lock after one minute by default. You can also change it to two, three and etc minutes or never activate.
How to adjust auto-lock timout on Surface RT
* From Start screen, wipe from right to open charms bar, select Settings > Change PC settings > Users, choose your Account and scroll down. Touch Require a password after the display is off for [x min].
* Enter “power plan settings” into search box from charms bar, you can also adjust the standard power sleep option in TURN OFF THE DISPLAY setting.