What it does
Holds an IOKit `kIOPMAssertionTypePreventSystemSleep` assertion so the Mac stays awake even when you close the lid. Required hardware (external display + power adapter) is enforced by macOS, not the app.
How it works
Closed-lid mode is a stronger assertion than display-sleep mode — it asks macOS to prevent system sleep even when the laptop signals lid-closure. macOS only honors this assertion when there's an external display attached and the Mac is on power; otherwise it's a no-op (your Mac will still sleep on lid-close, which is the safe behavior).
Where to find it
Settings → General → Keep awake when lid is closed.
When to use it
Closed-lid 'desktop replacement' setups, where you want the MacBook to keep running on its dock with the lid shut. Long backups or renders you want to run after closing the laptop.
How it compares
Amphetamine has a closed-display-mode toggle. Both apps need an external display + power; that's a macOS constraint, not something either app can bypass.
Tips
- On an iMac, Mac mini, or Mac Studio, this toggle is harmless — there's no lid to close.
- Pair with sustained-CPU and 'Allow display to sleep' for the rendering-while-closed combo.