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A tiny macOS menu-bar app that pins one microphone as the system default input. macOS likes to switch the default input to a Bluetooth headset's mic the moment it connects (which also drops the headset into low-quality HFP). MicPin keeps your chosen mic as the default and re-asserts it whenever something switches away.

1. Download MicPin-<version>.dmg from the latest release.
2. Open the DMG and drag MicPin into the Applications folder.
3. Launch MicPin from Applications. A microphone icon appears in the menu bar.

First launch — Gatekeeper. The app is open-source and ad-hoc signed (not notarized by Apple), so on first run macOS may say it "cannot be opened". Right-click the app → Open → Open, or run once:

xattr -dr com.apple.quarantine /Applications/MicPin.app

• Pick a microphone in the menu bar (or the settings window) to pin it.
• While the pinned mic is connected, MicPin keeps it as the default input — even when new devices connect or another app tries to switch.
• If the pinned mic is disconnected, MicPin does nothing; macOS chooses freely. When the mic reconnects, MicPin snaps the input back to it.
• To switch mics, pin a different one in MicPin. (A manual change in System Settings is reverted while the pin is active — that is the point.)

MicPin only reads device metadata and sets the default-input property. It never records audio and needs no microphone permission.

• macOS 26 (Tahoe) or later

Requires the Swift 6.3+ toolchain (full Xcode recommended).

git clone https://github.com/samplec0de/micpin.git
cd micpin
./scripts/bundle.sh     # builds dist/MicPin.app
./scripts/make_dmg.sh   # builds dist/MicPin-<version>.dmg

bundle.sh uses full Xcode automatically if only the Command Line Tools are selected. (To select Xcode globally instead: sudo xcode-select -s /Applications/Xcode.app.)

swift build      # compile
swift test       # run the core unit tests

If swift resolves to the Command Line Tools and swift test reports no such module 'Testing', prefix commands with the full toolchain:

DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer swift test

Open Package.swift in Xcode to debug.

• MicPinCore — pin logic behind an AudioSystem protocol, with a CoreAudio implementation. Devices are identified by their stable UID. The core is fully unit-tested with an in-memory fake.
• MicPin — AppKit menu bar (NSStatusItem) + a SwiftUI settings window.

MIT — see LICENSE.