It does. What do you think security researchers do both in their work/free time? You can clearly check that one by:

- Energy consumption lowers slightly in comparison to when it is waiting/"hearing" for the voice command.
- The voice command "Siri" is not sent to the network. It is one of the few commands that the device itself detects on its own. After it is activated, YES, it does send your audio to their cloud for analysis. They are not suppossed to legally save records of it not have been known any single known case where that has happened... But if you are paranoid about it, just don't fucking talk to Siri. DIsable it. You are good to go.

P.S.: If you ask siri for directions... YES, of course expect Siri (the cloud part of it) will remember that and show you related ads. It's clearly stated in the terms of use btw.

P.S.: There are additional reasons to disable Siri for reacting to voice starting because it has been exploited in the past by tricking it into giving access to the device as it was possible to access it without unlocking the terminal.