[maximente]

the device can't magically detect the world Alexa - there is some lossy process of translating incoming noise into a vector that has some probability of being the hotword, and above this probability the device enables.

a more accurate thing to say would be:

Alexa does not send data unless, in the course of listening for the hotword Alexa, it interprets some noise or utterance to be close enough to Alexa to start sending data