Sony Xperia Z3's camera is awesome, thanks to its both software and hardware features. Smile detection on Xperia Z3 camera enables you to take selfies automatically, as soon as one of the faces in the shot starts smiling.
Do as follows to enable Smile Shutter on Sony Xperia Z3 and Xperia Z3 Compact:
1. Open the Camera application and tap the 3dot icon on the top left to enter the settings
2. On the first tab, tap on the Smile Shutter option
3. Now you have 4 options to selects: Off, Small smile, Average smile, and Big smile
4. Choose the extent of the smile, you'd like the camera to identify and now it's time take automatic selfies.
** Note that you need to change the settings for the main camera and the front camera separately.