iOS: Siri, Apple's personal assistant for the iPhone 4S and above, can be a little bit of a chatterbox. Redditor iQuitter notes, however, that Siri has separate volume from the rest of your phone -- so if you want to turn her down, you'll have to do it independently of your ringer volume.It's pretty simple: you have a few different volume controls on your phone, including the ringer (which controls the sounds on your phone), the media volume (which controls the loudness of your music), and -- apparently -- Siri's volume.
If you've ever found that Siri beeps loudly even when your ringer volume is quiet, it's because Siri's volume is separate. Just open up Siri with the home button, then immediately turn the volume down to make her a little quieter. (This also turns down the voice button on your keyboard, which is easy to hit accidentally.)