The Unexpected Reboot
Desktop Macs (like the iMac, Mac mini, and Mac Studio) have a built-in energy saver feature designed for server environments. This feature is called “Start up automatically after a power failure.” If your home or office experiences a sudden power outage, and this feature is enabled, your Mac will automatically turn itself back on the second the electricity is restored.
While this is essential if you are running your Mac mini as a headless server in a closet, it is highly undesirable for a bedroom or home office computer. If the power flickers at 3:00 AM, you probably don’t want your iMac’s screen lighting up the room and the startup chime waking you up. For typical consumer use, you should disable this auto-boot behavior.
How to Disable Auto-Startup After Power Loss
You can toggle this hardware behavior in the Energy Saver settings.
- Click the Apple Logo in the top-left corner of your screen and select System Settings… (or System Preferences on older macOS versions).
- If you are on a desktop Mac (iMac, Mac mini, Mac Studio), click on Energy Saver in the sidebar.
- Note: If you are using a Mac laptop (MacBook) connected to an external display, this option usually does not exist because the battery acts as a built-in UPS, preventing sudden power loss.
- Look through the available checkboxes for the option labelled: Start up automatically after a power failure.
- Uncheck the box.
Now, if your building loses power, your Mac will stay completely powered off when the electricity is restored. It will only turn on when you physically press the power button.