Quick fish shell script to run a HASS trigger when a microphone is active on MacOS, in this case to turn an On Air light on and off.

com.onair.app.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.onair.app</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/local/bin/fish</string>
        <string>/opt/scripts/onair.fish</string>
    </array>
    <key>KeepAlive</key>
    <dict>
        <key>SuccessfulExit</key>
        <false/>
    </dict>
    <key>ThrottleInterval</key>
    <integer>1</integer>
    <key>StandardOutPath</key>
    <string>/opt/scripts/onair.log</string>
    <key>StandardErrorPath</key>
    <string>/opt/scripts/onair.log</string>
</dict>
</plist>

onair.fish

#!/usr/local/bin/fish

# Fish script to toggle Elgato Key Light Air and ON AIR light on or off dependant if the microphone is in use.
# Requires Home Assistant

# Create the variables for turning the light on and off. Bearer token created in your profile section in HASS
set bearer_token ''
set webhook 'http://192.168.x.x:8123/api/services'
set switch 'switch.on_air_light'
set light 'light.elgato_key_light_air'
set dir '/opt/scripts'

# Remove leftover files before starting
rm $dir/up $dir/down 2> /dev/null

# Build the onair function to run later
function onair
  set -l onair_status (ioreg -k IOAudioEngineState -n AppleUSBAudioEngine -c AppleUSBAudioEngine -rd 1 | grep -m1 -o  "\"IOAudioEngineState\" = 1" | wc -l | tr -d " ")
  switch $onair_status
    case '0'
      if not test -e $dir/down
        touch $dir/down
        rm $dir/up 2> /dev/null
        curl -s -X POST -H "Authorization: Bearer $bearer_token" -H "Content-Type: application/json" -d "{\"entity_id\": \"$switch\"}" $webhook/switch/turn_off > /dev/null
        curl -s -X POST -H "Authorization: Bearer $bearer_token" -H "Content-Type: application/json" -d "{\"entity_id\": \"$light\"}" $webhook/light/turn_off > /dev/null
      end
    case '*'
      if not test -e $dir/up
        touch $dir/up
        rm $dir/down 2> /dev/null
        curl -s -X POST -H "Authorization: Bearer $bearer_token" -H "Content-Type: application/json" -d "{\"entity_id\": \"$switch\"}" $webhook/switch/turn_on > /dev/null
        curl -s -X POST -H "Authorization: Bearer $bearer_token" -H "Content-Type: application/json" -d "{\"entity_id\": \"$light\"}" $webhook/light/turn_on > /dev/null
      end
  end
end

# Run script forever, but sleep after each run to conserve CPU
while true
  onair
  sleep 1
end