On the Sony Xperia Z3 and Xperia Z3 Compact, you can easily disable shutter sound to take pictures in silence. To turn off shutter sound on Xperia Z3, launch the default Camera application and do as follows:
1. Tap the 3dot button on the top left to open the Camera Settings.
2. Go to the third tab and make sure to turn off the Sound option
3. To bring back the shutter sound, simply turn the Sound option on.
While the Sound option in off, your pictures are taken in complete silence.