By default you can access Notification Center, Control Center, and Siri from the Lock screen of any iPhone or iPad, regardless of whether or not there's a passcode set. However, you can disable these options in the Settings app if you choose to. While Control Center access hasn't changed, many readers have been asking me how to restrict access to Siri and Notification Center in iOS 8 since they aren't seeing the options anymore. Fear not, they aren't gone, they've just moved!
How to turn off access to Notification Center and Siri from the Lock screen
Launch the Settings app on your iPhone or iPad running iOS 8 or higher.
Tap on Touch ID & Passcode.
Enter your passcode when prompted in order to continue.
Scroll down to the Allow Access When Locked Section.
Here is a brief description of what each option turns off if you toggle the option to Off —
Today View - Disable access to the today section of the Notification Center pulldown from the Lock screen, including widgets, calendar info, and any other data in the Today tab
Notifications View - Disable access to the Notifications tab of the Notification Center pulldown. This means no one can see any incoming notifications you receive if they pull down the Notification Center shade on the Lock screen
Siri - Disable access to Siri altogether until your iPhone or iPad is unlocked
Passbook - Disallows the use of any Passbook cards from the Lock screen unless the passcode is entered first
Replay with Message - iOS 8 allows you to quick reply to messages by pulling down on them. Turning this setting to Off guarantees that no one can respond to a message from your Lock screen unless a passcode is entered first.