Clamshell Mode with open lid in Mountain Lion


Since Lion (10.7) it hasn't been possible to use your external display as the primary and have the internal laptop display shut off. This "feature" was removed in favor of the so-called "Clamshell mode" where Apple decided that the only way to turn off the internal screen should be to close the lid.

Notice: As of OS X update 10.8.3 (released 15th of March), this app no longer works. Any prior versions should work just fine.

Why would you need to open the lid, if it's off?

There are several reasons. Some of them are:

1) Performance. The GPU is burdened by 2 active screens when lid is open. Even if you are only using 1 of them.

2) Wi-fi signal. Worse when lid is closed.

3) Heat. Will overheat more (and fan will come on) and worsen the life of your computer when the lid is closed. Opening it greatly increases airflow.

4) Digitizer sensitivity. Digitizers cursor will span horizontally over 2 screens, but vertically over 1. It will become more sensitive to minute movements and cause you to drag  stuff when you meant to just click. (Personal issue)

How to fix it

Instructions are simple: Close the lid. Launch the program. Open the lid. Press escape.

Download now

(To re-activate the display, Close the lid. Wait 5 seconds. Open the lid.)

The source code is also open.

Video demo

33 thoughts on “Clamshell Mode with open lid in Mountain Lion”

  1. updated to 10.8.3 and the clamshell app doesnt work anymore. any news/other workarounds on this topic?

  2. i van open my macbook for like 1/2 inch without waking the internal display. maybe that can help some of you while we waiting for a solution

  3. To Tiago Martins and gp1111:
    I've added a big yellow notice to this page. Apple has fixed the bug that I was exploiting to turn of the screen. I've currently gone back to using a tiny magnet, placed just below the left speaker, thereby fooling the mac into thinking that the screen is closed (the screen contains a magnet that sits on top of that point when closed).

    As I've emphasized in the Apple forums, using a regular magnet like that is of no danger to your computer. The screen already contains one. Try and hold a paperclip up to the black edge of your screen. It will stick.

  4. Hi seph,

    i just noticed your yellow box after my post went online but didn't want to spam another "oh there is a box, nevermind" post.
    i tried the magnet trick once but either i didnt catch the right spot on my white 13" macbook or my magnet was too weak, so ill give it another try now.

    if apple fixed the bug you managed to exploit then maybe now an official, non-workaround method is available? or maybe some of the older solutions that stopped working due to those bugfixes in the past are working again on 10.8.3? any news to that?

    im not only adressing you by my posts, but your blog happens to be quite a good communication base to this problem because its pretty easy to find doing a simple google search.


  5. Hi GP1111

    I am working on another program that does the same thing, except you will need to be running it all the time. I'll keep it minimal of course.
    It's not the most elegant solution, but it could be a solution for some people. The magnet trick will work for you, I can guarantee it. You just need to find the right spot (it varies from model to model). It took me a while to find mine the first time.


  6. i am not that much into programming, so correct me if im wrong, but from what i figure the impact of the magnet does change a boolean variable from "yes" to "no". and based on this setting the internal display is on or off. is thats the point where your trying to get a grip on it?

  7. GP, yes and no. I am trying to turn off the screen, but there's no specific feature like that in OS X programming as far as I can tell. The only way to do it, is to "grab" the display, like a computer game would. This blanks the screen and effectively disables it, but it's not entirely the same (application windows on the disabled screen are not moved to the other screen automatically).

    I will post an update when I have a program that works.

  8. thx for the details, although i dont wanna steal your time, its always interesting to reveal the the mayor thought behind an application, at least to me.=)
    will this new method have the same impact on the performance like it had in the outdated app or is it more about just darkening the screen on a visual level?

  9. Hello,
    I'm running on 10.8.2, I can't reactivate the display by closing for 5sec…

    When I launch the program, both screen goes black, I close the lid and wake the macbook with my mouse.
    But I can't reactivate the macbook display after that.

  10. Hi Tsu,

    You may be doing it the wrong way. You need to close the lid BEFORE you launch the program. Have a look at the YouTube video. You'll see me launching the app and then opening the lid. The instructions are:
    1. Close the lid (and wait for your mac to flash the screen to indicate it's now only running on the external display)
    2. Launch the program. Wait for your screen to go black (should happen almost instantly after launching) with a instruction text on it (you should only have 1 screen at this point, since you closed the lid already)
    3. Open the lid
    4. Wait 3 seconds. Press escape to quit the program or wait – it'll quit itself.

    Then it should work for you. It's the same instructions as in the article above. Be aware that upgrading to 10.8.3 will make this program unusable. Apple has fixed the bug that it exploited.

    GP1111: It will probably only be on a visual level, so the performance won't be as good as with the original app. The magnet trick is on a hardware level.

    – Seph

  11. Hi Tsu

    Then you are not using a display that your Mac supports running in clamshell mode, or you need to connect a mouse or keyboard before you do it. It's not related to this app, but to your setup. I can't really help you fix it, since I don't know what displays are supported by OS X.

    Sorry mate.

  12. Can someone please explain WHY apple keeps this like this? I mean why do they care about keeping it so tight a feature that when the lid is open the MacBooks display HAS absolutely to be on? I just don't get it! What is so important about this that they keep it that way?

  13. MacPap, only Apple can answer that – and they probably wont.

    My guess would be that it's counter-intuitive for "regular" users that the display is off when the laptop is open. In combination with this Apple dislikes adding configuration stuff just for the sake of pleasing power users like us.
    They would rather design it so there's better wifi-reception and ventilation when the lid is closed. I do believe the Retina mac has better ventilation (it's certainly different from the current models) but I honestly havn't done any tests.
    If the Retina laptop has better ventilation and wifi reception, then there would be less or no reason to run the laptop open with the screen off and thus the issue would eventually die out. Let's at least hope this is the case.

  14. Hey Seph, I'm on 10.8.3 and so I'm trying to use the magnet trick. I can get my external display to come on while my internal is asleep, however it only stays on for 2 or 3 seconds then turns off again! I've tried a bunch of magnet positions, nothing seems to be workin… I hope theres a way to fix it as Logic Pro can't run too well with 2 displays on. 🙁

  15. some people are having issues because they used the terminal hack before, but this method requires to undo the terminal hack….. just put :
    sudo nvram -d boot-args
    and reboot, and now you can use this app, because closing the lid wont turn off both screens anymore

  16. I tried your download, so my monitor would work in clamshell mode. It did not work. I see the monitor on, with my Macbook Pro lid open, but when I close the lid, my monitor goes blank. I have version 10.8.3 Mountain Lion. All worked well until 2 days ago. I checked all blue tooth and display settings, and all are set correctly, per all the help sites. Not sure if I am doing something wrong with your fix. Any help would be greatly appreciated.

    Thanks in advance

  17. Thx very much. But is there any solution in 10.8.3 or newer? In the future, if I want to upgrade Mavericks, is there any chance can use the Clamshell Mode? Thanks!

  18. Hello Charles

    I am not familiar with any solutions for 10.8.3 or newer. 10.9 (Mavericks) is arriving soon but from what I've read it's still not possible to disable the internal screen.
    I can only recommend using a magnet below the left speaker (placement varies depending on model). That's the solution that I use without issues.


  19. The magnet method is good but I'm afraid that the magnet will hurts the internal electronic devices. Am I wrong?

  20. Yes, you are wrong 🙂 There are already magnets inside your screen that does this exact thing when you close the lid. Go ahead. Test it. Hold a paper clip to the edge of your screen. There are certain places where it will stick – these are the places where there are magnets in your screen edge.

  21. According to YouTube:
    "nejtube1 year ago
    15" Retina MacBook Pros are a little over the bottom left portion of the left speaker and it's closer to the edge of the laptop."
    Ventilation is not an issue for my Retina MBP anymore. But there might still be advantages of having it open (some claim to see degraded WiFi performance in clamshell mode)

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