1. A computer-implemented method comprising: receiving audio data; determining, by a component of a mobile computing device that remains activated when the mobile computing device is in a low power state and before the component determines whether the audio data encodes a likely utterance of an entire predetermined activation term, that the audio data encodes a likely utterance of only a prefix predetermined activation term; and in response to determining, by the component of the mobile computing device that remains activated when the mobile computing device is in a low power state and before the component determines whether the audio data encodes a likely utterance of the entire predetermined activation term, that the audio data encodes the likely utterance of a prefix only of the predetermined activation term, activating a deactivated hardware component of the mobile computing device.