I had a closer look at several sensors and the ones I've seen, require a gas flow. Measuring gas in bag would saturate the sensor quickly, causing it to display a higher value than actual the actual CO contents. Not a real problem, since 1ppm is reason enough to discard the contents.
If there's a market, I can build them.
If meters are measuring and reporting out in parts per million (ppm) they all need some kind of means of measuring volume. Most use a flow, and the instruments are calibrated against that flow. This is why some of these meters are expensive; they must use a constant flow to measure the CO (or other gas) to get a concentration in unit volume.
The detector tubes do it differently, in that the gas is brought through the broken ends of the glass tube to a known volume in the hand pump. With this design, then the results are shown on a gradient gauge on the side of the tube, and usually there are two gradients, one for one pull of the pump, and one for more than one pull of the pump (3, if my memory is correct). This method is easier to do, but less accurate than the more expensive pumps (+ or - 5%, again if my memory is correct).
Now, a couple of more pieces of information. One great source of information on chemicals is the NIOSH Pocket Guide for Hazardous Chemicals. For carbon monoxide, it looks like this:
CDC - NIOSH Pocket Guide to Chemical Hazards - Carbon monoxide
Now there are several values here, the OSHA Permissible Exposure Limit (PEL) and the NIOSH Recommended Exposure Limit (REL). NIOSH uses available science, and us usually more up-to-date than the OSHA PEL, as OSHA must go through a regulatory process to set its PELs. Another organization, the American Conference of Governmental Industrial Hygienists (ACGIH) has its own set of standards called the Threshold Limit Value (TLV). This OSHA process sometimes takes years or even decades to modify. The NIOSH REL is usually lower than the OSHA PEL, but the ACGIH TLV is independently evaluated much more frequently than either of the other two standards, and industrial hygienists usually use the ACGIH TLV as their gold standard for exposures. Here’s what it looks like for CO:
OSHA PEL: 50 ppm
NIOSH REL: 35 ppm
ACGCIH TLV: 25 ppm
Now, this is for workers, not divers. Divers have this special problem of increased pressure. Remember your physics of diving classes? Remember Dalton’s Law of Partial Pressures:
Dalton’s law of partial pressures is a gas law which states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures exerted by each individual gas in the mixture. For example, the total pressure exerted by a mixture of two gases A and B is equal to the sum of the individual partial pressures exerted by gas A and gas B (as illustrated below).
Dalton's Law of Partial Pressures (Formula & Solved Problems)
Well, that changes as the pressure increases. So if a diver has 25 ppm (the ACGIH TLV) in his or her tank at the surface, and decides to dive to 99 feet (4 atmospheres absolute pressure) it would be as if that diver were breathing 100 ppm at the surface. If the diver was doing a deep dive, with 25 ppm in his or her tank, to 50 meters (6 atmospheres absolute pressure, or 165 feet depth) it is as if he were breathing 6 x 25 ppm, or 150 ppm CO.
Industrial Scientific has published information from the American Industrial Hygiene Association on symptoms at different concentrations of CO:
Carbon Monoxide Gas Detectors | CO Detectors | Industrial Scientific
What a log of newer diver don’t know today is that this sport almost lost Jacques Cousteau to CO poisoning in the 1950s. He describe this dive as “Our worst experience in five thousand dives did not come in the sea but in an inland water cave, the famous Fountain of Vaucluse near Avignon…”
He went on to describe the deteriorating dive:
…We had rapture of the depths, but not the familiar drunkenness. We felt heavy and anxious, instead of exuberant. Dumas was stricken worse than I. This is what I thought: I shouldn’t feel this way in this depth….I can’t go back until I learn where we are. Why don’t I feel a current? The pig-iron line is our only way home. What if we lose it? Where is the rope I had no my arm? I was able in that instant to recall that I had lost the line somewhere above. I took Dumas’s hand and closed it around the guide line. “Stay Here,” I shouted. “I’ll find the shaft.” Dumas understood me to mean I had no air and needed the safety aqualung. I sent the beam of he flashlight around in search of the roof of the cave. I found no ceiling.
Dumas was passing under heavy narcosis. He thought I was the one in danger. He fumbled to release the emergency lung. As he tugged hopelessly at his belt, he scudded across the drowned shingle and abandoned the guilde line to the surface. THe rope dissolved in the dark. I was swimming above, mulishly seeking for a wall or a ceiling, when I felt his weight tugging me back like a drifting anchor, restraining my search.
Above us somewhere were seventy fathoms of tunnel and crumbling rock. My weakened brain found the power to conjure up our fate. When our air ran out we would grope along the ceiling and suffocate in dulled agony. I shook off this thought and swam down to the ebbing glow of Dumas’s flashlight.
He had lost the better part of his consciousness. When I touched him, he grabbed my wrist with awful strength and hauled me toward him for a final experience of life, an embrace that would take me with him. I examined Dumas with the torch. I saw his protruded eyes rolling inside the mask.
The cave was quiet between my grasping breaths. I marshaled all my remaining brain power to consider the situation. Fortunately there was no current to carry Dumasaway from the pig iron. If there had been the least current we would have been lost. The pig iron must be near. I looked for that rusted metal block, mare precious than gold. Andy suddenly there was the stolid and reassuring pig Carlton. It’s line flew away into the dark, toward the hope of life.
In his stupor, Didi lost control of his jaws and his mouthpiece slipped from his teeth. He swallowed water and took some in his lungs before he somehow got the grip back into his mouth. Now,with the guide line beckoning, I realized that I could not swim to the surface, carrying the inert Dumas, who weighed at least twenty-five pounds in his waterlogged suit. I was in a state of exhaustion from the mysterious effect of the cave. We had not exercised strenuously, yet Dumas was helpless and I was becoming idiotic…
Cousteau, Jacques and James Dugan, The Silent World, Harper & Brothers Pumblishers, New York, Copyright 1953, pages 69, 76-78.
Obviously, both Dumas and Cousteau survived, and I’ll let you read the rest. But they were puzzled about how this all came about. Then they tested the air in their tanks. It was 1/2000 carbon monoxide, which if my calculations are correct, is 500 ppm.
In the book, The Silent World, Cousteau stated:
The next morning we sampled the cylinders. The analysis showed 1/2000 of carbon monoxide. At a depth of one hundred and sixty feet the effect of carbon monoxide is sixfold. The amount we were breathing may kill a man in twenty minutes. We started our new Diesel-powered free-piston air compressor. We saw the compressor sucking in its own exhaust fumes. We had all been breathing lethal doses of carbon monoxide.
160 feet / 34 feet/atmosphere (freshwater) = 4.7 atmospheres + 1 atmosphere = 5.7 atmospheres absolute pressure
5.7 atm x 500 ppm = 2350 ppm equivalent, = ~2350 ppm
If you follow the link above, you’ll see that the IDLH for CO (Immediately Dangerous to Life and Health for carbon monoxide) is 1500 ppm for 30 minutes under OSHA, and the Short-Term Excursion Limit under ACGIH is 400 ppm for 15 minutes.
They were very lucky to be alive at the end, and it’s worth reading the whole chapter.
SeaRat
Get one for $30, write the date on the back, and replace it in a year to avoid sensor drift. Send the old one to recycling. 
