macOS · CLI + Menu Bar

LED ON · NOISE CANCELLATION

Simulated — click the key. The real app moves your actual AirPods.

Caps Lock now controls your AirPods.

AirCaps remaps the physical Caps Lock key into a hardware switch for noise mode. LED on is Noise Cancellation. LED off is Adaptive or Transparency, your call — synced across the built-in keyboard and every Magic Keyboard on your desk.

View source See how it works ↓

Mechanism

Four steps happen before the LED moves.

01

Remap

hidutil turns Caps Lock into a no-op, system-wide, the moment the app launches. Text-input locking stops. So does the OS auto-driving the LED — nothing else is watching it anymore.
02

Listen

IOHIDManager watches for the key's raw down-transition anyway, underneath the remap, on every matched keyboard — built-in and every connected Magic Keyboard.
03

Automate

Accessibility drives Control Center's Sound popover: press Sound, wait for the dialog, expand the AirPods section, press the target mode's checkbox.
04

Illuminate

IOHIDDeviceSetValue writes the Caps Lock LED element directly, on every connected keyboard at once. The app owns the light now — it has to.

Internals

Eight things worth knowing.

HID

Raw HID capture

Reads keyboard input reports directly — independent of, and unaffected by, the hidutil remap sitting above it.

Control Center automation

No private API left to call, so it drives the same Sound popover a person would click through by hand.

N·KB

Multi-keyboard sync

LED state applies to every matched device at once. A keyboard that connects mid-session gets synced and remapped immediately.

TCC

Two-permission gate

Accessibility for the popover, Input Monitoring for raw HID. Both re-checked every time the menu opens.

LED

Explicit LED ownership

Once the remap is live, macOS stops driving the light entirely. Every state change is a direct write.

SPM

One shared core

Audio, Bluetooth, battery, and noise control live in a library that powers both the CLI and the menu-bar app.

DBC

Debounced state machine

Only idle or transitioning. A press mid-transition is dropped, not queued — the popover flow can't overlap itself.

CoreAudio switching

The same menu flips default and system output device between AirPods and built-in speakers.

Reference

The usage IDs this app touches.

Three HID usage IDs, one remap, and the three checkbox labels inside Control Center's Sound popover — that's the entire vocabulary.

HID usage table

Page	Usage	Meaning	Role
0x01	0x06	Generic Desktop → Keyboard	Matches every connected keyboard
0x07	0x39	Keyboard/Keypad → Caps Lock	The physical key being watched
0x08	0x02	LEDs → Caps Lock indicator	The light being written

Noise modes

Code	Control Center label	LED state
ANC	Noise Cancellation	On
AT	Adaptive	Off — default
TR	Transparency	Off — alternate

The remap, verbatim

hidutil property --set '{"UserKeyMapping":[{
  "HIDKeyboardModifierMappingSrc": 0x700000039,
  "HIDKeyboardModifierMappingDst": 0x700000000
}]}'

Reverted to {"UserKeyMapping":[]} on quit — or by hand, any time, with the same command.

Commands

The CLI underneath.

The menu-bar app is built on this. It works standalone too — aircaps [command], no menu required.

Command	Does
status	Shows connection, audio output, and battery — the default
on	Switches audio output to AirPods
off	Switches audio output to built-in speakers
toggle	Switches between the two
list	Lists every audio and Bluetooth device
ANC	Sets noise control to Noise Cancellation
AT	Sets noise control to Adaptive
TR	Sets noise control to Transparency

Setup

From clone to lit LED.

01

Build the CLI

make install — builds a release binary and copies it to /usr/local/bin/aircaps.
02

Bundle the app

make bundle-install — wraps the menu-bar app and installs it to /Applications.
03

Grant permissions

Accessibility for the popover, Input Monitoring for the key. The app's menu links straight to both panes.
04

Pick your off-mode

Settings — Adaptive or Transparency for when the LED is off. Adaptive by default.

Status

What's shipped, what's next.

Caps Lock → noise-mode toggle, LED-synced
Multi-keyboard sync, live on connect
CoreAudio output switching
Control Center automation for ANC/Adaptive/Transparency
Battery parsing via system_profiler
Reading current mode without opening the popover
Automated test suite
In-app updates
Bluetooth reconnect handling for on

Requirements

What you'll need.

macOS 13.0+ (Ventura or later)
AirPods Pro, or other AirPods with ANC/Adaptive/Transparency
Accessibility permission, for noise-mode switching
Input Monitoring permission, for the menu-bar app's Caps Lock capture

CoreAudio · IOBluetooth · ApplicationServices · IOKit HID · SwiftUI · Swift Package Manager

Four steps happen before the LED moves.

Remap

Listen

Automate

Illuminate