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How to stop HDMI showing your whole laptop screen

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Why it happens

Mac and Windows remember a mode for each screen and use it the moment you plug in. If that screen was last used for mirroring (Windows calls it Duplicate), your whole desktop appears on the wall: the open mail, the chat window, the notification that just came in.

Built-in fixes

On a Mac:

  1. Plug in, then open System Settings ▸ Displays, click the projector and set Use as to Extended display. macOS remembers this for that screen.
  2. In System Settings ▸ Notifications, turn off Allow notifications when mirroring or sharing the display.

On Windows:

  1. Press Win+P and choose Extend. Windows remembers this for that set of screens.
  2. In Settings ▸ System ▸ Notifications, under Turn on do not disturb automatically, tick When duplicating your display. On Windows 10 the same option is under Focus assist ▸ When I'm duplicating my display.

Both help, but only after the first time, and only for screens you've used before. A new projector in a new room starts from scratch.

Cover the screen first with Stagemark

Stagemark watches for new screens. The moment you plug one in:

  1. It covers the screen in black, before anything else can appear.
  2. If the screen came up mirrored, it switches it to an extended display.
  3. It asks what to do: Start output, Keep it black, Use as extended display or Use mirroring.

Tick Don't ask again for this monitor and it does the same thing next time with that projector. Stagemark recognises a monitor by its vendor, model and serial number.

FAQ

Does Stagemark cover my laptop screen?

No. It never covers the main display. Your laptop screen, menu bar, Dock and taskbar stay as they are.

What if I want mirroring for this one projector?

Choose Use mirroring when Stagemark asks. With Don't ask again for this monitor, that projector always mirrors.

Can I turn the cover off?

Yes. Untick Cover a connected monitor in black and ask in the Stagemark menu.

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