Tap on "Smart" on the home page and then tap on the "Add to Siri" button in "My Scenes".
If you want to learn more about "my scenes", please read the article How to create a scene.
Select the scene you want to voice control via Siri.
Edit a personalized phrase (e.g. I am away) to this Siri shortcut under "When I say".
When you say "Hi Siri, I am away", the scene of Leaving Home will be activated and you will also receive a push notification on your smartphone.
* Note: If the scene has been scheduled, Siri can activate the scene and the scene will run as scheduled.