At least on iOS, not without hacking the operating system. Siri’s ability to listen for a wakeword without an microphone indicator requires privileges that nor

At least on iOS, not without hacking the operating system. Siri’s ability to listen for a wakeword without an microphone indicator requires privileges that normal apps don’t get. On Android, as far as I can tell, the same is true, except that some phones ship with preinstalled third-party apps which can then get extra privileges.