A privacy bug reported by Brazilian site Mac Magazine allows someone to access hidden message notifications on a locked iPhone by asking Siri to read them …
As of iOS 11, you can set message notifications to be hidden on your Lock screen – you can see that a message has arrived, but its content is hidden. That setting is on by default on the iPhone X, where simply glancing at it will unlock the phone and allow the content to be displayed, while it can be set on other models.
However, a Mac Magazine reader discovered that Siri will read the content of most messages even though the content is hidden on the display.
Siri privacy bug lets it read out most hidden message content on a locked iPhone