Yes, the iPad Pro, iPhone 6s and iPhone 6s Plus all feature the option for an "Always-on Siri." The feature is the same as the "Hey Siri" option found in iOS 8, but your device does not need to be connected to a power source for it to work. Only devices with Apple's A9 chip support Always-on Siri. This means the iPad mini 4 and iPad Air 2 need to be connected to a power source for "Hey Siri" to work. You can lear how to enable "Hey Siri" in iOS 9 here.
Does the iPad Pro feature Always-on Siri?
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