Mac not detecting an external monitor? Fixes that work
Short answer: check the monitor's input source, then try a different cable and port — many USB-C cables carry charging only, not video. Open System Settings → Displays and hold Option to reveal Detect Displays. If you already have one external display on a MacBook with a base M1 or M2 chip, that is the most it supports.
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Start with the monitor
- Input source — use the monitor's buttons to pick the input you plugged into (HDMI 1, DisplayPort, USB-C). Many monitors do not switch by themselves.
- Wake it — some monitors sleep so deeply that they miss the Mac. Turn the monitor off and on at its power button.
- Wake the Mac — press a key or move the mouse; a sleeping Mac will not light a new display.
The cable is the usual culprit
USB-C cables look alike but differ inside. A cable that came with a phone or a charger often carries power and slow data only — no video. Use a cable sold for video: a Thunderbolt cable, a USB-C cable marked for DisplayPort or video, or the one that came with the monitor.
- Try each port on the Mac. On some MacBook Pro models only certain ports drive a display at full resolution, and a hub on one port may behave differently on another.
- If you use an adapter (USB-C to HDMI, for example), try the Mac without it, or a different adapter.
- Plug the cable in firmly at both ends, and unplug and replug it once the Mac is awake.
Use Detect Displays
- Open System Settings → Displays.
- Hold the Option key. A Detect Displays button appears.
- Click it while still holding Option.
If the monitor is listed in Displays but shows nothing, check it is not set to mirror a display that is asleep, and that its resolution and refresh rate are ones it supports.
How many displays your Mac supports
This catches many people with a second monitor. MacBook Air and 13-inch MacBook Pro models with a base M1 or M2 chip support one external display. A second one plugged in is simply ignored. Newer and higher-end chips support more — Apple lists the exact number for each model in its technical specifications, under Display Support.
Docks and DisplayLink adapters
A dock that promises two screens on a base-chip MacBook usually uses DisplayLink, which needs Synaptics' DisplayLink Manager app installed and allowed under Privacy & Security → Screen & System Audio Recording. Without it, the extra screen stays black.
If nothing else works
- Restart the Mac with the monitor connected.
- Test the monitor and cable with another computer, and the Mac with another monitor, to find which part is at fault.
- Check Software Update: display fixes often arrive in macOS updates.
Once it is working, stop the Dock jumping between screens and learn how to switch a monitor off without unplugging it.
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Frequently asked questions
Why is my Mac not detecting my monitor?
Most often it is the cable — many USB-C cables carry no video — or the monitor is on the wrong input. Base M1 and M2 MacBooks also support only one external display.
Where is Detect Displays on a Mac?
Open System Settings, Displays, and hold the Option key; the Detect Displays button appears.
Can a MacBook Air run two external monitors?
Models with a base M1 or M2 chip support one. Later models support more; Apple's technical specifications list the number for each.
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