Interesting, I didn't know this about ISS. I've fought a tiring battle to get my CO2 levels below 500ppm consistently, and it's night and day compared to the 800-1200ppm I used to measure. Can't even imagine what 5000ppm is like!
I work in a very small office shed, and if I leave the door and window closed tight it will quickly get over 2000 ppm (45-60 min). At that point I'm typically feeling more tired, and a bit foggy.
By keeping the window cracked I can keep the readings down in the 800-1100 range, and I feel much better.
In particular I find I am much less groggy in the mornings, and stepping outside doesn't feel like a breath of fresh air.
The changes I made are not options for most. I have an industrial rooftop HVAC unit for a space about 5x larger than my home. The fans run continually and there is no fresh air exchange per se but part of the return duct runs through the attic which is not air-tight, more of an open cavity. I change the air filter every 3 months and keep the returns clean by vacuuming regularly. I try not to close doors to encourage circulation, and my bedroom door had an vent to the hall above it -- not sound or light proof, but doesn't restrict airflow.
The key that I've found is airflow. A closed room and a bunch of fans won't help you, but circulating the air of your entire home will make a big difference. It's important that your home breathes. An airtight home is actually very unhealthy, though heating/cooling is more efficient.
Lastly, cooking is the worst offender for poor air quality. Having a stove-top exhaust hood that actually filters and vents outside is so important. Cooking without exhaust or fresh air can easily bring the kitchen and surrounding areas near 1000ppm in under an hour. I keep my exhaust vent on more often than not and it makes a big difference. Negative air pressure is good: air is pulled in from outside.
So just curious for my own designs, how certain are you about those ppm numbers you listed?
I'm thinking that the specific CO2 concentrations matter if one wants to relate the readings to various research on human mental performance.
Also, I am finding products that seem to require an Android or iOS device to work: no. They must be independent. If they had a webserver, nice idea, but all connections should be unrequired and switchable to off.
I would have assumed CO2 from the context, but since you mentioned cars I'm wondering if you mean CO, VOCs, and/or PM32.
Unless your car has the fans off and the windows rolled up for a really long time, I'd be surprised if CO2 was something you need to worry about. Maybe if you're sleeping in it with the windows rolled up?
CO in the house is definitely a concern. If you have a fireplace, woodstove, or furnace with a properly functioning chimney, you're unlikely to run into problems AFAIK. But people die every winter because they used a propane grill, or kerosene heater, or gas stove/oven in their house without proper ventilation. Or used a wood stove with ineffective / blocked chimney. So in colder climates having a functioning CO meter seems like a no-brainer.
In the house, similar awareness could be beneficial.
But I have not yet found a decent product. It is unacceptable that one is supposed to have a Google account or similar in order to read a ruler or configure a blender.
Sometimes I've had similar lines of questioning. Where it occurs to me that something might be a risk worth addressing, and so I'd better gather data until I'm confident everything is okay or that I'll have a way to notice when the risk becomes real.
Every(?) time I've gone down that route, I later concluded that the concern really wasn't that big a deal, and that I'd just be hyper-focused on it because of anxiety or A.D.D. I.e., in the overall scheme of things, the true risks that deserve priority are pretty evident: good sleep and body weight, exercise, not smoking, keeping my finances in order, etc. I have a tendency to forget those primary issues when I start focusing on something that could, potentially, under some circumstances become a problem.
When I go down those rabbit trails, I end up reading a lot of articles, buying some unnecessary stuff from Amazon, planning for a project that realistically I'd never complete, and just worrying a lot.
If there's any takeaway from all this (for me, at least), it's "don't sweat the (probably) small stuff".