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I don't use the CAPS LOCK functionality in OS X, so I disabled the key under the system preferences. Now that key is completely useless to me - ok, I could map the CMD/CTRL/ALT key to that key, but I already got keys for that…

So what I have in mind is to use the LED on the key (I use the recent Apple wireless keyboard) to annouce if I've got mails waiting… something like that. Is it possible to control the LED directly? Controlling it via an objective-c cocoa app is okay, I'll write that app by myself, but until now, I can find anything useful from Apples cocoa documentation.

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I guess that's more or less hardwired into the keyboard firmware, so you'd have to crack that first. –  slhck May 18 '11 at 7:49
I use Seil (formerly PCKeyboardHack) to not only disable Caps Lock's default functionality (which is useless) but also to set it to another key, and in turn I use this key heavily in the command line as a generic command key (a sort of overloaded context switching functionality). It's really useful. 2 years later, I started wondering how to control this green LED light that's also on this key that I had forgotten about. –  Steven Lu Jul 21 '14 at 23:52

2 Answers 2

up vote 4 down vote accepted

One Python example: http://www.psychicorigami.com/2009/03/01/5k-morse-code-app-using-capslock-led/

It is possible. I am trying to find an app that I found years ago, that could toggle the num lock and caps lock LEDs on my old iBook (10.4). Found that while looking today.

Found it.

Needs to be compiled though.

Oh, and HID LED test tool – Xcode example :D

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Thanks. As a note: Only the last example (Xcode) works on the current Mac OS X 10.6. –  DASKAjA May 24 '11 at 7:35
Well, the last example is listed as 10.5 on Apple's page. Yet the morse code app is based on that code and won't work on 10.6. Don't know about the keyboard_leds one, but I sure hope it does. –  cde May 24 '11 at 7:53

Here's another tool to control keyboard leds under OSX: https://github.com/busyloop/maclight

MacLight lets you control the keyboard-LEDs (capslock, numlock) on your Mac.

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