Previously, Karabiner has the feature to automatically disable the internal keyboard when your external keyboard connected so you can easily put it on the top of your internal keyboard without worrying about the key conflicting. But now Karabiner is no longer working with MacOS Serria so the author Tekezo is remaking it as Karabiner-Elements, this developing Karabiner-Elements have not included the mentioned feature above yet, but it allows you to modify it karabiner.json configuration in order to map keys of any keyboards. So I did a hack to make this happen again so I can keep placing my favourite Filco Minila Air on the Apple Internal Keyboard again.

• Your Internal keyboard identifiers.
• Your External keyboard identifiers.

Notes: You can easily find these when connected both keyboards, set some settings in Karabiner-Elements then they will show up in ~/.karabiner.d/configuration/karabiner.json through profiles.devices.

• Use my karabiner.json in this project, it contains all the rules to Disable all Keyboard buttons.
• Replace the devices section by your current devices you got above in Step 1.
• Make sure all devices are set with ignore: true so it this configuration is not activated by default.

• Install node js >= 4.x (directly or nvm or whatever).
• Copy my script disable-internal-when-external-connected.js to some place you like.
• Remembering in Step 1, You got the product_ids of your internal keyboard and external keyboard. In my case, my internal keyboard product_id is 628 and my external keyboard product_id is 34050.
• Now run command:

EXTERNAL_KEYBOARD_ID=[product_id of external] INTERNAL_KEYBOARD_ID=[product_id of internal] node disable-internal-when-external-connected.js

• E.g. in my case it will be :

EXTERNAL_KEYBOARD_ID=34050 INTERNAL_KEYBOARD_ID=628 node disable-internal-when-external-connected.js

That's it, now it will automaically disable your internal keyboard when your external keyboard is connected and it will re-enable your internal keyboard when your external keyboard is disconnceted. Woo hooo!

Any feedback is welcome!

Happy Hacking!