This just is not true if distracted and many if not most OOAs are a result of some distraction. It may be true of your regulator, your regulator may need a tune up or an upgrade. But any one of my regulators will go to near flat ZERO and it might not be until the last couple of breaths that I might notice, but if distracted, possibly not. And what is one going to do with a couple of breaths?From my experience, the regulator will let you know that you’re closed to OOA. It’ll get harder & harder to inhale from the regulator----
I have run out of air, one time, circa 1984. It was before octopus rigs were really standard and having learned to dive in 1966 and my wife in 1979 neither of us were set up on an octopus much less a long hose (for open water). And at the time (and still) I commonly used a dh regulator. We were in Fort Lauderdale, drift diving. I had been given the buoy to tow and my wife and I were asked to buddy with this lady we did not know. She hit the water swimming and mostly up current. I kept trying to herd her in and she kept turning into the current and swimming. I was so distracted by her that I was totally surprised when my Tekna T2100 simply quit. The spg read ZERO. I never noticed anything. We were somewhere over 80 feet, maybe close to 100 feet. My wife was down current of me and I signaled to her I was OOA. She made a beeline for me and we buddy breathed to about 60 feet where I let her go and did a slow CESA. The lady, she swam off to Cuba I guess, do not remember. The DM and captain threatned to ban me (what is new, I have been banned from Florida near a dozen times) when I politely explained to them that their diver that they stuck us with was HORRIBLE and should never have been certified and they are the ones who certified her. And I pointed out to them I was not an instructor at the time, was not a professional so why the HXXX did they stick us with her to begin with. That shut them up. But, a good, well tuned regulator, will go to zero or so nearly so and do it such that if distracted, a diver may not realize it until it is too late.
The fellow in the video linked to, maybe if he would quit arm swimming and dog paddling his air consumption would improve.
James