Mobile phones (well, at least iPhones and Android phones) are "always listening" for their wake words in exactly the same way that the Echo is "always listening

Mobile phones (well, at least iPhones and Android phones) are "always listening" for their wake words in exactly the same way that the Echo is "always listening." They are doing local signal processing to detect a wake word (phrase) and, upon detection, they stream audio to cloud-based service that performs ASR and NLP on it in order to perform some service on behalf of the user.