eli5: How does siri hear me say “hey siri” if it isn’t constantly listening to my conversations or me speaking?

Question

eli5: How does siri hear me say “hey siri” if it isn’t constantly listening to my conversations or me speaking?

In: 17336

Answer 1

Better question why does Siri randomly go “Uh huh?” or “I’m not sure, here’s a search result?” in the middle of the night? That’s the real question.