I wasn't aware that the Xperia E3 had this feature, I thought it was the Z3 series only
http://blogs.sonymobile.com/2014/09/11/333-things-you-didnt-know-the-xperia-z3-series-could-do/
More with gestures
Double tap screen to wake features again, as does Smart call handling – turn your Xperia Z3 orXperia Z3 Compact on its face to silence an incoming call or bring it up to your ear to answer. And, Smart backlight control keeps the screen on when you are holding your Xperia in your hand; it will stay lit when you are looking at a photo without touching the screen. When you are not holding the device, the screen turns off (according to your sleep setting).
