If it were me, I'd do this:
We have our meter, a disconnect box (which is the main disconnect), then our first panel (which, by code, is a sub-panel). From that first panel, I feed our garage with a 50amp breaker.
I'd pull the main disconnect and wire an LED to one or both of the legs in that first panel just above the main breaker for that panel. Then I'd run the wire for the LED up to our kitchen and put it in a box by the counter (the main brain central station of our house).
Then I'd install the key in that first panel and its counterpart in the garage panel.
Then I'd turn it all back on.
So, if power goes out, the LED is out.
I pull the key, disconnect the first panel, walk out to the garage, install the key, turn it, and turn on the generator equipment.
When power comes back on, the LED will light up.
I'd go back out to the garage and reverse the process.
Someday, I may do that. :thumbsup: