Starting with iOS 9, you are able to shut Siri up as easily as turning the mute switch to silent. Prior to iOS 9, Siri would not respond to the state of the ringer switch.
Indeed, how many times did you wish you could chat with Siri in the middle of the night but didn't out of fear her loud voice might wake up your significant other?
As it turns out, a quick trip to the Settings app and a couple of taps is all it takes to tell Siri to honor the state of your ringer switch.