Interactive logon: Machine inactivity limit

Windows notices inactivity of a logon session, and if the amount of inactive time exceeds the inactivity limit, then the screen saver will run, locking the session.

Policy path: 

Computer Configuration\Windows Settings\Local Policies\Security Options

Default: 

Not enforced.

Supported on: 

Windows 8, Windows Server 2012

Registry settings: 

Not a registry key

Reboot required: 

No