Doesn't it have to listen to everything to capture the wake word "hey siri"? How else is it done?
The iPhone has dedicated low-power on-device hardware that is trained to pick up "Hey Siri" exclusively. It only wakes up the rest of the device and captures additional audio after that wake word has been triggered.
>pick up "Hey Siri" exclusively
until it isn't. anything apple is proprietary and any feature could silently change at any time even for only specific devices/user.
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