Enable Lock Screen, and Monitor Power save mode on Pi 3. The default is manual screen locking either via menu, or keyboard shortcut, and Monitor power save mode will actually turn off the monitor (not screen blank it). Default for power save mode in 20 min.
All settings can be customized/adjusted for preference, and monitor power save can be completely disabled if so desired, so that it never turns off, or goes into power save mode.
Install Instructions: https://drive.google.com/file/d/0B2X5T2P-KI8memRhOGY5djNoOFk/view?usp=sharing&pageId=100974448756156510051