Siri, the virtual assistant on iOS and Mac, can be handy, but if you don’t use it or want to turn Siri off for another reason, it’s easy to do so. Use the Settings app on your iPad or iPhone, or System Preferences on a Mac, to disable Siri.
How to Disable Siri on iPhone or iPad
To turn off Siri on an iOS device running iOS 11 or later, go to Settings > Siri & Search and turn off each of the following options (the buttons will turn white when turned off): Listen for “Hey Siri,” Press the Home button for Siri, and (if you see it) Allow Siri When Locked. Confirm with Turn Off Siri.
Turning off Siri on iOS 10 requires a slightly different process. Go to Settings > General > Siri and toggle Siri off. Tap Turn Off Siri when prompted to confirm your choice.
Since disabling Siri means you can no longer use voice commands on an iOS device, it makes sense to also disable dictation on your iOS device, as it will no longer work. This is also necessary if you want to delete all of your voice data from Apple's servers.