Do not be surprised with the tip. Users can turn on an option in setting that make Siri to obey the broader iPhone and iPad hardware mute switch.
Enable Siri Muting & Unmuting with the Hardware Switch on iPhone & iPad
Settings ---> General ---> Siri ---> Voice Feedback ---> Select Control with Ring Switch
Leave Settings and activate Siri with the mute switch enabled, Siri will respond in text and on screen only, without blabbing the answer to the world. By this, Siri works exactly the same as it did before, but you won’t hear any voice feedback if the mute switch is toggled on.
Silence Siri with the Mute Switch
Flipping the Mute switch will make Siri completely quiet in responses.