"Hey Siri" lets you use your iPhone or iPad hands-free.
As long as it's plugged in and within range of your voice, all you have to do is say the magic word and Siri will wake-up and wait for your question or command. It's great for the iPhone when you're in bed or in the car, or the iPad when you're cooking in the kitchen or wondering around the house. It's voice activation for your voice control!
How to enable Hey Siri on your iPhone or iPad
Launch the Settings app on your iPhone or iPad.
Tap on General.
Tap on Siri.
Turn On the option for Hey Siri.
How to use your iPhone or iPad hands-free with Hey Siri
Make sure your iPhone or iPad is plugged into a charger.