Moving the mouse to a corner of the screen randomly triggers sleep or Mission Control
You're just moving your mouse to the corner of the screen to hit a scrollbar and suddenly the screen locks, or Mission Control explodes open, or the desktop appears. It's alarming and disruptive and feels like the Mac is haunted.
Why does this happen?
macOS has a Hot Corners feature that triggers actions when your mouse hits a screen corner. Some Macs ship with hot corners pre-configured, and even when blank, third-party apps or previous settings can activate them without you realizing.
How to fix it
System Settings → Desktop & Dock → scroll down to the Hot Corners button.
Click it to see what's assigned to each corner.
Set any corners you don't want to – (dash/nothing) to disable them.
Tip: you can hold a modifier key like ⌥ before a hot corner triggers — configure this to reduce accidental activations.
Discussion
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