Avoid triggering Hot Corners accidentally – Mac OS X Hints

Many of us use Hot Corners (accessed from System Preferences -> Mission Control or System Preferences -> Desktop & Screen Savers) to trigger various actions. On my Mac, slamming the mouse to the bottom right corner reveals the desktop; the bottom left corner triggers Mission Control. You can also use the corners to trigger things like Notification Center, Launchpad, starting a screen saver, or putting your display to sleep.

But anyone who uses Hot Corners (which OS X refers to interchangeably as Active Screen Corners) triggers those mouse-controlled shortcuts accidentally sometimes. The solution is this: When you’re choosing a Hot Corner setting from one of the drop-down menus, hold down your preferred modifier key or keys. You’ll see the options change from, say, Mission Control to Option Mission Control” instead.

From then on, your corner will only work when you’re also holding down the modifier key(s) you specified. Now, trips to the Apple menu won’t trigger your Hot Corner shortcut—unless you’re pressing your selected modifier key, too.

via Avoid triggering Hot Corners accidentally – Mac OS X Hints.