Hey Siri is a new "iOS 9", feature... AKA
Siri 2.0. I downloaded 9 to my phone... but I understand the tablets have the same feature.
Pretty slick! I updated this morning. I had to set-up the hey Siri in settings. Then train it/her to recognize "MY" voice. Now.... As long as my phone is in it's charger.... Siri listens for "me" to say "hey Siri" followed by a command/request like what's todays weather forecast. Or call "so-and-so" (someone in my contacts). Siri will dial the number and put the call on speaker.
I have a phone dock on the table beside my favorite easy chair. So if I am watching TV or on-line (laptop) the phone is charging.
If I turn off the lock screen.... it will open my X10 app. or TV remote app. But Siri can't click the buttons (yet).