Make sure you are doing it correctly. There was a little correction needed from the my original post. You are focusing on breathing outward only being sure that your lips are tightly closed. If you can can breath outward even though your mouth is fully closed, then you will be dreaming, confirm by using a second RC. If you cannot breath outward, you are not lucid and your cheeks should swell with air.

I tried this several different ways in my last lucid. I became lucid by using this method, then tried the RC several different ways.
It worked as expected every time on slow semi-forceful exhale. Inhale was very unreliable and when attempting to switch between nose breathing and mouth breathing I was having problems determining if I was breathing out with enough force. When clearly focusing on breathing outward though my mouth, I was able to every time even though my lips were tightly closed. There is no mistaking where I am breathing from when I do it this way. Let me know how further testing goes. Do not use this RC as your only RC until you have used it successfully enough to know it works reliably for you.