Why not simply allow us to use the various Siri products by their generally odd names? "Hey Siri" depends on a human brain to call out the "Hey..." As such, that brain knows which device it is calling. So instead of trying to make the devices best guess which one the brain wants to respond, why not let the brain do that processing- getting it right 100% of the time- and call out a unique name either given or assignable to each device? For example,
"Hey Homepod" would not be confusing to Macs, watch, phone, tablet or AirPods. The human wants Siri on HP to respond. And- like Siri- Homepod is an odd enough name, it's not going to accidentally come up in daily conversations to then accidentily activate Siri on Homepod.
"Hey AirPods" would not be confusing to Macs, watch, phone, tablet or HPs. Same benefits.
"Hey iPhone"
"Hey iPad"
"Hey iMac"
Or, how about getting really crazy and allow us consumers to rename Siri on select devices, encouraging us to choose odd names so that we are not accidentally summoning Siri in casual conversation. "Hey Joe" might not be a good name but "Hey Rasputin" probably works. Maybe Stark's "Hey Jarvis"? "Hey KooKooKaChoo"?
Bottom line: the summoning brain ALWAYS knows which device it wants to respond. So shift that AI to just BI (biological intelligence already debugged & fully functional) and use it. No need overthinking the obvious.*
*Important disclosure: I do NOT "have $2XX Billion in the bank," nor did I stay as a Holiday Inn Express last night.