The report claims that the new iPhones could come with an always-on “Hey Siri” function. This means that you can say, “Hey Siri” whenever you want without having to touch the phone. Prior to this, the feature could be enabled in the Settings menu, but would only be applicable if your iPhone was plugged in.
Presumably this is done to save battery as the phone would have to keep listening out for the hotword. Google has already introduced a similar feature in the form of “OK Google” awhile ago, so we wouldn’t be surprised if Apple were to introduce it as well. It is unclear if this feature is limited to the new iPhone 6s and 6s Plus as it could potentially require new hardware.
However based on the iOS 9 betas released so far, there has been no evidence to suggest an unplugged “Hey Siri” function, so it really could be an iPhone 6s/6s Plus exclusive. Either way we will find out more tomorrow so do check back with us then for the details!