In 11.2.6 and iOS beta version of iOS 11.3 found a bug, because of which Siri can read all comers content, messages on the lock screen. This applies only to third-party applications such as Gmail and Facebook Messenger. In the case of the standard services of voice assistant will ask first to unlock the device.
For example, if you tell Siri voice message from Gmail, the assistant will read not only text, but also a subject and sender's name. Saying "Hey, SiriĀ» does not necessarily - just hold down the home button.
The problem is particularly acute for owners iPhone X. When using Face ID notifications on the lock screen to hide the flagship until the user unlocks it with the help of his face. But if you can just ask Siri voice message, it is the use of such protection no.
While Apple does not eliminate the vulnerability, it is recommended to turn off notifications on the lock screen for all major email clients and instant messengers. You can also disable Siri to work when the phone is in sleep mode.