If you've got a passcode set on your iPhone, Siri and Passbook will still work by default on your lock screen. This means that anyone who wants to talk to Siri or use one of your passes will still be able to. While it's convenient, it can be a bit unsafe. If you prefer having to use your passcode in order to access them, you can do so easily with a simple settings change.
Launch the Settings app from the Home screen of your iPhone.
Tap on General.
Tap on Passcode Lock and type in your passcode when prompted.
Under the Allow Access When Locked section, turn the Siri and Passbook options to Off.
That's it. You'll now be required to enter your passcode before using a Passbook or Siri feature from the lock screen.