This is a huge moment for home automation.- Tim Cook
I lift up my ᴡᴀᴛᴄʜ and say, "Hey Siri, open the garage door." What is actually happening? The ᴡᴀᴛᴄʜ is sending that audio through Bluetooth to my iPhone, which sends it up through my AT&T LTE connection to iCloud. iCloud processes the audio and sends it back down, through my iPhone to my ᴡᴀᴛᴄʜ. My ᴡᴀᴛᴄʜ will then use handoff to pass the command back over Bluetooth to my iPhone.
Now my iPhone processes the HomeKit command and once again sends the HomeKit request up through AT&T LTE to iCloud. iCloud is going to send it down through my AT&T U-verse connection, to my Apple Airport Extreme* which passes it via WiFi to my Apple TV which is serving as my HomeKit hub.
AppleTV relays the message over WiFi back through the Airport Extreme's wired ethernet connection to my macOS server which is running Homebridge. Homebridge then uses MyQ Chamberlain APIs to ask the garage to open - so that means a message is sent off the macOS server back out of my home to the MyQ server.
The MyQ server pushes the request back down into my house through the WiFi over the MyQ garage door module which then sends the standard radio waves to my garage door opening and the garage opens.
This amazing process takes about 1 second. Light goes really fast.
* Technically I have two Airport Extremes to extend the network, so there's yet another handoff going on.