After some additional reading, since the prevailing wisdom is that humans are not able or very good at detecting low blood oxygen.
It appears that the human body has some capacity to detect low blood oxygen levels more or less directly. Many articles. Peripheral or central chemoreceptors, possibly something else.
https://www.britannica.com/science/human-respiratory-system/Chemoreceptors
'
Peripheral chemoreceptors
Hypoxia, or the reduction of oxygen supply to tissues to below physiological levels (produced, for example, by a trip to high altitudes), stimulates the carotid and aortic bodies, the principal arterial chemoreceptors. The two carotid bodies are small organs located in the neck at the bifurcation of each of the two common carotid arteries into the internal and external carotid arteries. This organ is extraordinarily well perfused and responds to changes in the partial pressure of oxygen in the arterial blood flowing through it rather than to the oxygen content of that blood (the amount of oxygen chemically combined with hemoglobin). The sensory nerve from the carotid body increases its firing rate hyperbolically as the partial pressure of oxygen falls. '
'The carotid body communicates with medullary respiratory neurons through sensory fibres that travel with the carotid sinus nerve, a branch of the glossopharyngeal nerve. Microscopically, the carotid body consists of two different types of cells. The type I cells are arranged in groups and are surrounded by type II cells. The type II cells are generally not thought to have a direct role in chemoreception. Fine sensory nerve fibres are found in juxtaposition to type I cells, which, unlike type II cells, contain electron-dense vesicles. Acetylcholine, catecholamines, and neuropeptides such as enkephalins, vasoactive intestinal polypeptide, and substance P, are located within the vesicles. It is thought that hypoxia and hypercapnia (excessive carbon dioxide in the blood) cause the release of one or more of these neuroactive substances from the type I cells, which then act on the sensory nerve. It is possible to interfere independently with the responses of the carotid body to carbon dioxide and oxygen, which suggests that the same mechanisms are not used to sense or transmit changes in oxygen or carbon dioxide. The aortic bodies located near the arch of the aorta also respond to acute changes in the partial pressure of oxygen, but less well than the carotid body responds to changes in the partial pressure of carbon dioxide. The aortic bodies are responsible for many of the cardiovascular effects of hypoxia'
http://blogs.discovermagazine.com/neuroskeptic/2009/12/14/in-the-brain-acidity-means-anxiety/
There is more. Undoubtely, when properly executed the helium or argon method will work in most cases. I'm not that average though, and can't afford additonal brain damage. (survival)
Being in a locked room full of argon or helium will kill you, but that'snot the same as an exit bag.
Anyway, if anyone feels like exploring this topic ...
It appears that the human body has some capacity to detect low blood oxygen levels more or less directly. Many articles. Peripheral or central chemoreceptors, possibly something else.
https://www.britannica.com/science/human-respiratory-system/Chemoreceptors
'
Peripheral chemoreceptors
Hypoxia, or the reduction of oxygen supply to tissues to below physiological levels (produced, for example, by a trip to high altitudes), stimulates the carotid and aortic bodies, the principal arterial chemoreceptors. The two carotid bodies are small organs located in the neck at the bifurcation of each of the two common carotid arteries into the internal and external carotid arteries. This organ is extraordinarily well perfused and responds to changes in the partial pressure of oxygen in the arterial blood flowing through it rather than to the oxygen content of that blood (the amount of oxygen chemically combined with hemoglobin). The sensory nerve from the carotid body increases its firing rate hyperbolically as the partial pressure of oxygen falls. '
'The carotid body communicates with medullary respiratory neurons through sensory fibres that travel with the carotid sinus nerve, a branch of the glossopharyngeal nerve. Microscopically, the carotid body consists of two different types of cells. The type I cells are arranged in groups and are surrounded by type II cells. The type II cells are generally not thought to have a direct role in chemoreception. Fine sensory nerve fibres are found in juxtaposition to type I cells, which, unlike type II cells, contain electron-dense vesicles. Acetylcholine, catecholamines, and neuropeptides such as enkephalins, vasoactive intestinal polypeptide, and substance P, are located within the vesicles. It is thought that hypoxia and hypercapnia (excessive carbon dioxide in the blood) cause the release of one or more of these neuroactive substances from the type I cells, which then act on the sensory nerve. It is possible to interfere independently with the responses of the carotid body to carbon dioxide and oxygen, which suggests that the same mechanisms are not used to sense or transmit changes in oxygen or carbon dioxide. The aortic bodies located near the arch of the aorta also respond to acute changes in the partial pressure of oxygen, but less well than the carotid body responds to changes in the partial pressure of carbon dioxide. The aortic bodies are responsible for many of the cardiovascular effects of hypoxia'
http://blogs.discovermagazine.com/neuroskeptic/2009/12/14/in-the-brain-acidity-means-anxiety/
There is more. Undoubtely, when properly executed the helium or argon method will work in most cases. I'm not that average though, and can't afford additonal brain damage. (survival)
Being in a locked room full of argon or helium will kill you, but that'snot the same as an exit bag.
Anyway, if anyone feels like exploring this topic ...
