siri has itself trained to a single user's voice. I've never had anyone else's voice activate my phone with "Hey Siri". Admittedly, it usually takes me saying "Hey Siri" 3 times before it recognizes my voice, but I'm 100% certain a radio ad would get no response from my phone.
Siri is definitely not trained to a single voice. And yes, the car radio can turn it on. I've had a podcast discussion of Siri trigger it. It became such a joke that some podcasters have another phrase they say when they mean "hey Siri".
Since the iPhone 6S, Hey Siri is activated by a dedicated chip in the SoC. This enables low-power real-time detection of trigger words. Before, Hey Siri only worked with phones in the process of charging, because it was done with software, so a lot less efficient.
These voice-activated chips can be trained (as seen in a lot of other phones), but I'm not sure the software-powered Siri can be trained.
Doesn't "trained" in the context of voice recognition mean something more like "better able to understand your voice" and not "able to exclude other voices."
Just want to chime in and say that I can activate my girlfriends iPhone by saying "Hey Siri" in a girly sounding voice. It's trained to only her voice but I can trigger it. So it's not foolproof as you make it seem.
My wife's phone regularly (maybe once a month), starts listening in response to me saying something, which isn't even "Hey Siri", despite never training with my voice. My voice does not sound anything like my wife's.
So, I think the error rate is simply not low enough to make conclusive claims about what it might or might not do.
