Smart Stay is a feature of the Galaxy S III that keeps the phones screen on while you’re looking at it, using thew front facing camera to track your eyes. This means that while you’re reading something, your screen will not time out. Once you look away, it will be allowed to time out. So why should this feature stay exclusive to the Galaxy S III?
Developer elnoxvie has created the app Smart Stay EX, which emulates this feature but works on many other phones. So if you want this awesome app, there is a lite version on the Play Store (along with a paid pro version). Hit the source link for more info and to download it!