meeting-watcher

Posts to MQTT when you join or leave a call on macOS — for driving a busy light, a Home Assistant automation, a "do not disturb" sign.

Swift, single binary, no third-party dependencies (the MQTT client is a small hand-rolled publisher over Network.framework).

How it works

Every call app shares one reliable signal: microphone use. On macOS 14+ CoreAudio's process API reports which apps hold the mic, and since we only read audio-graph state (never capture samples), this needs no microphone permission — and no permission prompt of any kind.

By default any app on the mic means you're in a meeting — Meet, Slack huddles, Zoom, Teams, FaceTime, whatever — or you can restrict it to a list of apps (see Which apps count). MicMonitor watches per-app mic input via CoreAudio property listeners, so it reacts the instant the mic turns on or off; a periodic poll catches any listener edge that gets missed.

MQTTClient publishes state changes retained, plus an availability topic backed by an MQTT Last Will, so the broker marks you offline if the watcher dies or drops off the network.

Build & run

Requires macOS 14+ and the Xcode Command Line Tools (xcode-select --install) — no full Xcode or SwiftPM.

./build.sh                           # compiles ./meeting-watcher with swiftc
cp config.example.json config.json   # edit for your broker
./meeting-watcher                    # run the watcher
./meeting-watcher --once             # print current state as JSON and exit

Configuration

config.json (see config.example.json), looked up in the working directory and next to the binary. Environment variables override the file:

Env var	Meaning
MQTT_HOST	Broker host (default localhost)
MQTT_PORT	Broker port (default 1883)
MQTT_USERNAME	Broker username
MQTT_PASSWORD	Broker password
MQTT_BASE_TOPIC	Base topic (default presence/<user>/meeting)
MQTT_CLIENT_ID	MQTT client id
MQTT_TLS	1 to enable TLS
POLL_INTERVAL	Interval for re-checking mic state in case a CoreAudio event was missed, seconds (default 5)
MEETING_APPS	Comma-separated app filter (empty = all apps)
HA_DISCOVERY	0 to disable Home Assistant discovery
HA_DISCOVERY_PREFIX	Discovery prefix (default homeassistant)

baseTopic supports %{username} (default) and %{hostname} placeholders.

Which apps count

apps is empty by default, so every app holding the mic counts. Set it to report only on specific apps:

"apps": ["Slack", "Chrome", "zoom", "Microsoft Teams"]

Entries are matched case-insensitively as substrings of the app name, so Chrome catches "Google Chrome" and zoom catches "zoom.us" — you don't need the exact name. MEETING_APPS="Slack,Chrome" overrides the file; MEETING_APPS="" clears the list back to "all apps".

Run ./meeting-watcher --once while a call is live to see the names to filter on in detail.mic_apps.

MQTT topics

For base topic presence/<user>/meeting (username of whoever runs the process):

Topic	Payload
presence/<user>/meeting	Retained JSON (full state, below)
presence/<user>/meeting/state	ON / OFF — convenient for a binary sensor
presence/<user>/meeting/availability	online / offline (LWT-backed)
homeassistant/binary_sensor/<id>/config	Retained HA discovery config

{
  "in_meeting": true,
  "detail": { "mic_apps": ["Slack", "zoom.us"] },
  "user": "patch0",
  "updated_at": "2026-08-05T14:15:58Z"
}

Run at login (launchd)

examples/com.meeting-watcher.plist runs the watcher as a per-user LaunchAgent and restarts it if it dies (KeepAlive). Edit the paths in it — ProgramArguments and WorkingDirectory to match your clone, and StandardOutPath/StandardErrorPath to match your home directory (launchd does not expand ~) — then:

cp examples/com.meeting-watcher.plist ~/Library/LaunchAgents/
launchctl bootstrap gui/$(id -u) ~/Library/LaunchAgents/com.meeting-watcher.plist

launchctl kickstart -k gui/$(id -u)/com.meeting-watcher   # restart (e.g. after ./build.sh)
launchctl bootout gui/$(id -u)/com.meeting-watcher        # stop / uninstall

KeepAlive means launchd restarts the process whenever it exits, so bootout is the only way to actually stop it. Re-bootstrap after editing the plist.

Logs go to ~/Library/Logs/meeting-watcher.log (connection + publish activity) and ~/Library/Logs/meeting-watcher.err. A healthy log shows TCP connected…, then MQTT connected (CONNACK ok), then a Published: line per state change.

Home Assistant

No YAML needed. The watcher publishes an MQTT Discovery config on every connect, so as long as HA's MQTT integration points at the same broker, a binary_sensor appears by itself under a Meeting Watcher device:

homeassistant/binary_sensor/<object_id>/config   # retained discovery config

<object_id> is the resolved base topic with every character outside [a-zA-Z0-9_-] replaced by _ — HA silently ignores discovery topics containing anything else, and usernames commonly contain dots. So presence/patch0/meeting gives presence_patch0_meeting, which is also the entity's unique_id, so it survives restarts without duplicates.

The full state JSON is wired up as json_attributes_topic, so mic_apps is available as an attribute if an automation wants to know what's holding the mic:

{{ state_attr('binary_sensor.presence_patch0_meeting', 'mic_apps') }}

Discovery settings live under discovery in config.json:

Key	Default	Meaning
enabled	true	Publish the discovery config
prefix	homeassistant	Must match HA's discovery prefix
name	In a meeting	Entity name
deviceName	Meeting Watcher (%{hostname})	Device name in HA

name and deviceName take the same placeholders as baseTopic. Disabling discovery publishes an empty payload to the config topic, which tells HA to remove the entity — otherwise the retained config would linger forever.

Manual configuration (if discovery is disabled)

mqtt:
  binary_sensor:
    - name: "Patrick In A Meeting"
      state_topic: "presence/patch0/meeting/state"
      availability_topic: "presence/patch0/meeting/availability"
      payload_on: "ON"
      payload_off: "OFF"
      device_class: running

Notes / limitations

• With no apps filter, anything holding the mic counts, so dictation or a voice memo also reads as "in a meeting". detail.mic_apps says what's responsible; set apps if you want to narrow it.
• Publishes at QoS 0 — fire-and-forget, which is what you want for frequently-updated presence state with a retained last value.