Unless your computer is in a secure space that is accessible ONLY BY YOU, you must run a screen saver that will automatically lock your screen after 15 minutes of inactivity and require a password to unlock it.

This is necessary to prevent an unauthorized person from being able to see sensitive information or exploit access to your computer in your absence.

See instructions below for how to set your screen to lock automatically for Mac or Windows devices:

Mac

How to Set Your Computer to Lock Your Screen Automatically

1. From the Apple menu, choose System Preferences.
2. Click Desktop & Screen Saver.
3. Click Screen Saver, and then use the slider to choose 15 minutes (or less). 
4. Click Show All to go back to the main System Preferences window.
5. Click Security, and then click Require password to wake this computer from sleep or screen saver.
6. Close the System Preferences window.

When your computer has been inactive for the set interval, the screen saver starts. Your password is required to start using the computer again.

How to Set Up a Hot Corner to Lock Your Screen Manually

Next, set up a Hot Corner so you can quickly activate the screen saver when you leave your computer.

1. From the Apple menu, choose System Preferences.
2. Click Desktop & Screen Saver.
3. Click Screen Saver, and then click Hot Corners.
4. Click the list next to the corner of the screen you want to use as a hot corner and select Start Screen Saver, and then click OK.
5. Close the System Preferences window.

How to Lock Your Screen Manually

If you've set up a Hot Corner using the previous procedure, you can use this procedure to lock your screen without waiting for the screen saver to start.

1. Move your mouse to the corner you set up as your Hot Corner.

The screen saver starts. Your password is required to start using the computer again.

Windows

How to Set Your Computer to Lock Your Screen Automatically

When you leave your computer, it’s best to start a screensaver that can only be turned off with a password.

In Windows 10:

1. Click the Start menu, then Control Panel (gear icon).
2. Click Personalization, then Lock Screen.
3. Optionally, choose a Background option from the dropdown list
4. Optionally, choose apps that will display status information while the screen is locked (for example, Alarms and Clock or Weather). Click a square with a plus in the middle and then click one of the Windows apps from the pop-up list to add it. To stop showing an app on the computer's lock screen, click its icon, then choose None from the pop-up list.
5. Optionally, click Show lock screen background picture on the sign-in screen.
6. Click Screen timeout settings, then selecting values from the Screen and Sleep dropdown lists to set how long it takes for your screen to lock or go to sleep.

When your computer has been inactive for the set amount of time, the screen saver starts. Your password is required to start using the computer again.

How to Lock Your Screen Manually

Use this procedure to lock your screen without waiting for the screen saver to start. It is recommended to do this whenever leaving your computer unattended.

1. Press the Windows logo key + L.
2. Click the mouse or touch any key to show the sign-in screen.
3. Sign back in using your password (on managed computers, this will be your Cornell password).