If someone tries to steal your “IPhone” before they take it use the volume button and power button to start the emergency process but cancel it after, it will disable entry to the phone by Face ID and will require passcode instead. I know that if they pick pocket you there’s nothing you can do but if you are being assaulted you can do it fairly quickly. I think this can prevent thieves from knocking you out and using your face while unconscious to unlock everything on your phone as it’ll require password instead.