OS X Mountain Lion: Require a password after waking your Mac
To keep the information on your Mac secure when you are away from it, set it to require authentication when it wakes from sleep. When you return to your Mac, type your login name and password to continue working.
- Choose Apple menu > System Preferences, click Security & Privacy, and then click General.
- Select “Require password for sleep and screen saver.”
You can adjust the amount of delay before a password is required in the pop-up menu.
To lock your screen quickly with fast user switching enabled, choose Login Window from the menu with your user name. Your apps and documents remain open and undisturbed, but your computer is locked.
Locking the screen doesn’t prevent other users from turning off the computer, restarting it, and logging in to their own accounts. If you think this could happen, be sure to save your work before you leave your computer.
You can use your administrator name and password to unlock the screen for yourself or a standard user, but not for another administrator.