MicGuard

Prevents Bluetooth audio devices (e.g. AirPods) from hijacking the default macOS microphone.

Beta: MicGuard is pre-1.0. Backward compatibility is not guaranteed until version 1.0.0 is reached.

Requirements

• macOS 15+

Install

brew install pszypowicz/tap/mic-guard

Build from source

make install

How it works

MicGuard is a macOS menubar app that monitors the default input device via CoreAudio. When the system switches the input (e.g. when AirPods connect), MicGuard immediately reverts to your preferred microphone.

On first launch the current input device becomes your preferred mic, and "Launch at Login" is enabled automatically. To disable MicGuard, quit the app.

Features

• Menubar app - runs silently in the background with a shield+mic icon
• Auto-revert - reverts unwanted input device switches caused by Bluetooth connections
• Self-contained - no config files, no CLI; settings live in macOS defaults

Demo

AirPods connecting hijacks your input device. MicGuard reverts it instantly.

Modes

MicGuard has two device enforcement modes, switchable in the menu bar menu:

Auto (default)

Protects your preferred mic during device connect/disconnect events. If you switch the input device in System Settings after devices have settled, MicGuard recognizes this as intentional and saves the new choice as your preferred mic.

Manual

Always reverts to your chosen preferred device, no matter when or why the switch happened. Uncheck Auto Mode in the menu bar menu to pick a device.

Configuration

All settings live in macOS defaults under the cz.szypowi.micguard domain:

Key	Purpose
preferredDevice	Exact name of your preferred input device
mode	auto or manual - device enforcement strategy (default: auto)
settleSeconds	Seconds to wait before accepting a device switch as user-initiated (1-30, default: 2)

defaults read cz.szypowi.micguard                          # inspect
defaults write cz.szypowi.micguard settleSeconds -float 5  # tune settle period (no UI)
defaults delete cz.szypowi.micguard                        # reset everything

Status broadcast

For personal integrations (e.g. SketchyBar), MicGuard posts read-only telemetry. There is no way to control or query MicGuard externally - it only tells:

• cz.szypowi.micguard.statusChanged - distributed notification posted on startup and whenever the current input device or its muted state changes; userInfo: device (name), muted ("true"/"false" - volume 0 or hardware mute flag)

Debugging

MicGuard logs to the unified logging system with subsystem cz.szypowi.micguard:

log stream --predicate 'subsystem == "cz.szypowi.micguard"' --level debug           # follow live
log show --predicate 'subsystem == "cz.szypowi.micguard"' --last 1h --info --debug  # past logs

In fish, log is a builtin - use /usr/bin/log.

Notes:

• When a Bluetooth device connects or disconnects, CoreAudio fires DEVICE_LIST_CHANGED and DEFAULT_INPUT_CHANGED two or three times per event. Duplicate log lines are normal macOS behavior; the handlers are idempotent.
• Running the raw binary (/Applications/MicGuard.app/Contents/MacOS/MicGuard) bypasses the LSMultipleInstancesProhibited duplicate-instance check - quit the running instance first. Logs go to the unified log, not stderr.
• Development loop: make dev builds the bundle and (re)launches it, make dev-stop kills it.

Common issues:

• Preferred mic not found - if the preferred device is disconnected, MicGuard keeps monitoring and switches back when it reconnects.
• Login item not starting - check System Settings → General → Login Items; re-toggle "Launch at Login" in the menu bar menu. Launching MicGuard manually re-registers the login item.
• Reset - defaults delete cz.szypowi.micguard, then relaunch; the current input device becomes the preferred mic again.

Releasing

The app version comes from the latest git tag: scripts/bundle.sh stamps git describe --tags into Info.plist (the source plist keeps a 0.0.0-dev placeholder). Builds are ad-hoc signed; the Homebrew cask's postflight clears the quarantine flag on install.

1. Tag and push - CI builds the app and attaches MicGuard.zip to the release:

   git tag v<version>
   git push origin v<version>

2. Compute the checksum:

   curl -sL https://github.com/pszypowicz/MicGuard/releases/download/v<version>/MicGuard.zip | shasum -a 256

3. Update version and sha256 in Casks/mic-guard.rb in homebrew-tap.

4. Verify with brew update && brew upgrade mic-guard.

License

MIT