The real problem is that Alexa and Siri increase your attack surface area to include every speaker in your home--including any cheapo Bluetooth or internet-conn

The real problem is that Alexa and Siri increase your attack surface area to include every speaker in your home--including any cheapo Bluetooth or internet-connected speakers that could get hacked to produce these human-inaudible sounds. (To be fair, I recall this specific point coming up in an HR thread about Alexa being able to open your door for Amazon deliveries, but I thought it was worth reiterating here.)