By skyforbes Interesting thing I just noticed today when I tried to ask a question starting with "Hey Google" why driving and the response was she couldn't understand which I thought was highly unusual for Gemini. Turns out Android Auto acts the same as Google Nest Hub devices is that (at least currently on mine) even if your Assistant App setting is set to Gemini it's still using Google Assistant. I assume the rollout of Gemini to smart devices, when it hits me will fix the issue with Android Auto.
Interestingly, while driving, I can use the long power button press on my Samsung S23U running latest OneUI and Android 16 to launch Gemini into Voice mode instead of Google Assistant.
They way I know for sure the Hey Google works to launch Gemini on my phone while not driving and doesn't if I say it while driving is I can ask a question then after it responds, open the Gemini app to see if the conversation is there. And you can also tell by the difference in the voice. Hey Google on Google Nest or Android Auto won't show the conversation in your Gemini history because it's not actually using Gemini.