The CapsLock indicator of password fields is not being exposed to ATs -- at least in Gtk+. I believe this may also be true for OS X. (@Chris, please confirm.)
Steps to reproduce in OS X (I'm using 10.11.2 and Safari built from source just now):
1. Load this Layout Test in Safari: https://trac.webkit.org/browser/trunk/LayoutTests/accessibility/gtk/entry-and-password.html
2. Launch VoiceOver
3. Tab to the text input field
4. Press CapsLock twice quickly to toggle CapsLock on
5. Tab to the password input field for which the CapsLock indicator is displayed
Expected results: VoiceOver would announce the fact that CapsLock is on.
Actual results: VoiceOver doesn't announce the fact that CapsLock is on.
Examining the accessibility tree using XCode's Accessibility Inspector, I see:
-> AXTextField:AXSecureTextField [see note 1]
-> AXGroup [see note 2]
Based on the highlighting done by the Accessibility Inspector:
note 1: This is the entire input widget which holds the text input area, the CapsLock indicator, and a key with a drop-down indicator.
note 2: This is the text input area.
@Chris: If I'm wrong about the above, let's slap an [ATK] in the Summary and update the OS. But if I'm right, it would be nice to have a cross-platform solution for exposing this to ATs.