Siri has been updated in iOS 8 to be always listening...at least while plugged in. Just shout out "hey Siri" and Siri will respond without touching the device. Siri can also now listen to music being played and identify the artist and song name with Shazam-like functionality. Just ask Siri to listen and she will help.
See the video below showing this functionality.
If there is a passcode, Siri can be disabled and this access will not function.