M1 MacBooks and Open Clamshell: Thumbshell Mode

I’ve had an M1 Max¹ MacBook Pro for a little more than a year. What I’ve liked about is that it’s very, very quiet. Even when it’s in full clamshell mode, the fans rarely gear up. On my old MacBook Pro 17″ I’d found some boot ram arguments which allowed clamshell mode with the lid wide open.

I also like the stereo speaker system, which substitute well for desktop audio when Open clamshell would be ideal for M1 Pro and M1 Max MacBooks.

I’ve been looking for a similar boot ram argument for the M1 Max. I can’t find it anywhere. The closest is Lunar app about which I’ve already written in some depth. My conclusion is that I don’t like the idea of mirroring the monitor and turning brightness all the way down. It’s still driving the graphic card at double speed for no reason, with all the heat that entails.

It turns out that Lunar creator Alin Panaitu likes his method for screen blackout even less than I do. He’s written an in-depth article which describes his voyage looking for exactly the kind of neat solution I’m seeking where the internal screen is turned off in clamshell mode.

For anyone interested in how Apple is locking us out of our own computers, built on what was an open-source foundation, Panaitu’s article is an eye-opener. No matter which way he or we turn, Apple won’t allow us to set our internal screen to off unless we close the lid.

What is particularly annoying is how Apple took away the last of the sensible hardware workarounds. It used to be possible to tell a MacBook Pro that the screen was closed with magnets. Not anymore.

…the lid was detected as being closed using magnets in the lid, and some hall effect sensors. So you were able to trick macOS into thinking the lid was closed by simply placing two powerful magnets at its sides. With the new 2021 design, the MacBook has a hinge sensor, that can detect not only if the lid is closed, but also the angle of its closing. Magnets can’t trick’em anymore.

Panaitu has worked for four days on this problem, going through about five different API’s, disabling both SIP (csrutil disable in Recovery Mode) and Apple Mobile File Integrity, via boot argument: sudo nvram boot-args="amfi_get_out_of_my_way=1". Turning off SIP is no big deal, but turning off AMFI is strong voodoo and does make a Mac more vulnerable. It should also give Panaitu a free hand to make those API’s he discovered work, using code injection via another boot argument and Frida:

 sudo nvram boot-args=-arm64e_preview_abi

No dice.

Apple, either let us turn off the screen when in clamshell mode, or open up the API’s to let Panaitu build a tool which will do it for us.

If there’s someone at Apple who knows the boot arguments necessary for open clamshell mode on M1 Pro and M1 Max Apple Silicon MacBooks, please leave an anonymous comment here for the rest of the world.

In the meantime, I’m still using my thumbshell method. It helps with:

1. heat. Even a slender air vent lets a lot more heat out than no air vent. Hence fans come on much later and at a lower RPM.
2. screen keyboard burn. For design reasons, Apple has made the fit between keyboard and screen on its MacBook Pros too slender. What happens is the screen presses down the keys. This suits Apple as the screeb on any recent MacBook Pro is ruined within a few years and any self-respecting designer or photographer or well-heeled businessman or woman will want to buy a new one. This keyboard imprint on the screen is worst when the screen is heated up in closed clamshell mode. The thumb method stops any keyboard imprint.²

What the thumb clamshell method doesn’t help enough with is are the speakers. The sound still isn’t nearly as good as in open clamshell but on a scale of ten:

• open: 9
• closed: 2
• thumb clamshell: 6

The sound is much better with the lid open just a bit. Not really good enough for music but adequate for dialogue and YouTube videos.

A big thanks to Alin Panaitu for sharing his in-depth research into closed clamshell method with the whole world. Any other programmer attempting to solve this issue with either enjoy a huge headstart. For others Panaitu will have saved him or her days of wasted time: no need to do the preliminary footwork and tests to learn that his or her method is a dead end.

If anyone does discover the boot argument which works (there should be a boot argument solution, based on past history), please let me know.

Alec Kinnear

Alec has been helping businesses succeed online since 2000. Alec is an SEM expert with a background in advertising, as a former Head of Television for Grey Moscow and Senior Television Producer for Bates, Saatchi and Saatchi Russia.