I did a quick google to answere a few lingering questions I had and learned a few things in the process:
-I had no idea its not required to say 'Check'. Seems to me the proper thing to do is say it, but I guess not. That'll be news to my best friend who about bit my head of a few years back in a casual game!
-It is the opponent's responsibility to point out a flag fall- I resigned the game my time ran out (I had thought this the case, but it seems to be in my interest ot not point it out in the future)
The one thing I didn't find a clear answer to is what to do when my opponent doesn't push the clock?
In the game I resigned on time, there were several times my opponent didn't push the clock. He was not a beginner, which I have seen it advised to remind the opponent to push their clock. In a couple cases, I hadn't realized he didn't push it until I went to hit the button and discovered a free move. (Too bad I didn't make better use of the time!)
But in two instances, iirc, I noticed, pondered a bit and made my move anyway. I didn't wan to sit there and stew over propriety.
What's the correct response?