Quickly Enter Clamshell Mode with an External Display in Mac OS X

Jun 8, 2012 - 13 Comments

Clamshell MacBook in a Book Arc

Keeping a portable Mac turned on while the lid remains closed is commonly referred to as clamshell mode. This basically docks the MacBook Air/Pro/etc and allows the GPU to power an external display only which can help performance of some games and graphics intensive tasks. There are several ways to enter into clamshell but this is probably the fastest for those who use an external keyboard or mouse with a MacBook.

  1. Connect the external display and an external keyboard or mouse to the MacBook Pro or Air
  2. Close the lid of the MacBook
  3. With the lid closed, click the mouse button or hit a keyboard key
  4. The MacBook will awake and the external display will turn on, becoming the primary display

This should work in all versions of OS X without any issues. Be aware that running a MacBook with the lid closed reduces the ability for the Mac to dissipate heat through the rear fan ports and the keyboard which could theoretically lead to overheating, making clamshell best used in well ventilated areas or with a Mac that’s placed in something like a TwelveSouth BookArc, which is what’s holding the MacBook in the image above.

If you open the lid at this point the displays will flicker blue and both screens will turn on, that can be prevented if you’d rather keep the internal display turned off, or you can go with it and set the primary display to tell the Mac which screen to use for the menu bar, Dock, and where windows will default to open to.

Thanks for the tip Jared

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Posted by: Paul Horowitz in Mac OS X, Tips & Tricks

13 Comments

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  1. Ryan says:

    Isn’t this meant to be bad for the laptop as the fan blows out on the inside ???

    • Paul says:

      Not necessarily though it could be, it really depends on the ventilation and how the Mac is situated.

      A lot of people report increased speeds using clamshell with games and Photoshop, the Book Arc product page cites a few reviews that demonstrate noticeable Photoshop performance. It’s probably best to use it in a cool or air conditioned environment so you don’t overheat the MacBook in question though.

  2. frankie says:

    Not sure what happened with my lion, but i can’t activate clamshell mode that easy as before.
    If I connect my ext. display when the mbp’s lid is closed and click/press a key, it activates the ext. display as extended, not as a single display [internal screen still detected by OSX and "in use"].
    So I need to open the lid, find the restart button on the mbp’s screen and close the lid.
    Then the ext. display goes gray and now the internal screen is disabled.
    Any quicker solution?

  3. Dekard says:

    MBPs don’t dissipate any significant amount of heat through the keyboard. No matter how often that misconception is posted, it’s still a misconception.

    • Jay says:

      Absolutely correct. There is no threat to overheating with the machine’s lid closed as long as there ventilation around the unit.

  4. João Chua says:

    Clamshell mode only works on my MBP when connected with the power adapter. And, when I read the instructions for clamshell mode on the Apple site (http://support.apple.com/kb/HT3131), it requires the adapter to be connected. Is it just me, or did this article NOT mention anything about the power adapter requirement?

    • Justin says:

      You are correct. I wish there was a terminal command where the macbook doesn’t need to be connected to power when in clamshell mode.

    • Doug says:

      Thanks João!

      I was going crazy for hours trying figure out what I was doing wrong. The power connector is the key! You’d think Apple would put that in their instructions for clamshell mode!

      Doug

  5. Justin says:

    I use my Macbook Air in clamshell mode all the time (along with the book arc mentioned in this post). One annoying thing about this feature is that you have to have it connected to power at all times. Does anyone know how to do this without having the machine connected to AC power?

    The reason, I don’t always want my machine to be connected to power as I’ve heard this is not good for the battery…

  6. ptsash says:

    The NVRAM method etc no longer work in Mountain Lion. I found a solution, though:
    1) Do a restart, then close the clamshell while waiting for the restart to complete
    2) The Macbook will detect the external display during the restart, and will use it as the primary (and only) display
    3) Once the restart is completed (with the external display used as primary display, open the clamshell. The built-in display will remain off, but you can now use the keyboard and touchpad. Voila!

    • felicitycubed says:

      Didn’t work for me running Mountain Lion on my Mid-2009 MBP, paired with a Mid-2008 24″ Cinema Display.

      What i did do though, with a little tweaking and elbow grease, and i really mean a little, was to modify an April 2010 post by Paul Horowitz, found above in this post under “set the primary display”.

      I did as follows:

      1) Open Up Display Prefs
      2) Bring up your external monitor and click “Arrangement”
      3) Deselect “Mirror Displays” if not done so already
      4) As Paul Horowitz outlined, click and drag the white menu bar to the external display.
      5) For me, the resolution on the Cinema Display switched over to its native 1920×1200, but the pointer still resided on the MBP’s built-in display, in some sort of suspended animation, if i do recall correctly. I think the built-in display lost its menu bar to the Cinema Display, but open windows remained at the MBP’s native res.
      6) So, to bring everything in-line, i selected “Mirror Displays” and then deselected it again and the coveted result was finally at hand.

  7. Raoul Duke says:

    Is there a way to charge my iphone while my macbook is closed???

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