Is it possible to hook or add a trigger for when Google assistant is activated upon saying "Hey Google"?
Here's a scenario, I have a smart light and I want it to give feedback when google assistant is triggered by changing it into red for few seconds upon invocation of the phrase "Hey Google".
Not really.
Since you tagged this "google-assistant-sdk", you can make a device that uses the SDK and triggers when it responds to the hotword. But if you're building your own device, you can use other software that triggers based on the hotword without using the SDK.
Other than that - no, you can't do this. You can only be notified when your own Action or your Smart Home device is specifically invoked.
