It's exciting that I've found a way to check my breath meditation that works for me, and that I think works for you. But, I had a lot of failed attempts.
What Works
It's simple. I just keep asking, "Is this the breath?" And I limit myself to two answers. "This is the breath." or "This is not the breath." And I keep repeating this.
What doesn't work
I've tried many things, and they don't work, at least not consistently. Unfortunately, the things that don't work don't fail 100% of the time. They work sometimes. And, in a measurement tool, a ruler that works sometimes is not a good ruler. Here are some things that I've found don't work.