An earcon is a great idea! Your intuition of where to wire it up is correct:
deactivate would let you trigger your earcon when listening starts and ends, respectively. As far as how an earcon would work with SpokestackTray, you can listen for the
DEACTIVATE events (https://github.com/spokestack/react-native-spokestack-tray#spokestacklistenertype-enum). Alternatively, you could tie the earcon to the tray opening and closing with
Finally, you might be aware Tray uses the platform ASR by default (unless you specify otherwise), which on Android means that the Android ASR will play the Google earcon unless the Android device user has disabled it in their settings.