Update for iOS 11
With iOS 11, you can still bypass the iPhone lock screen and trick Siri into getting into a person's phone. The bypass is the same as it was in the earlier version of the operating system:
- Press the home button using a finger not associated with your fingerprint authentication, prompting Siri to wake up.
- Say to Siri: Cellular data.
Siri then opens the cellular data settings where you can turn off cellular data.
As was the case before, anyone can do this. It doesn't have to be the person who "trained" Siri.
By also turning off Wi-Fi, you cut off her connectivity access. You will get an error saying, “Siri not available. You are not connected to the internet.” But you don’t care about that error because you have already bypassed the iPhone lock screen.