That's because it's $$$$. CO2 is hard to measure (it's inert!), and only recently advances in NDIR allow us to measure it directly. Those are still $50, and that's just component cost.
PM2.5 is also around $50 for decent parts.
Another $10 for T/H/P. Another $20 for cheapest LCD you can find.
Ok, so we are up to $130, but now you gotta pay for manufacturing ($$$), PCB, hardware development, calibration, testing, mechanical design... Probably $200-$300 total depending on quantity.
So, let's say you can make the whole device for $250 just in costs. Now you gotta add software (BT\Wifi code is not fun!), shipping, overhead, profits. So, you gotta sell this thing for $350+.
Would you buy one for $350?
https://www.omega.com/en-us/test-inspection/air-soil-liquid-...
[1] https://www.airgradient.com/open-airgradient/instructions/
In case you're not aware, the kit was upgraded this year to move the temperature sensor a little further away from heat sources, they now bundle enclosures with the kit (if requested), and also sell [0] pre-soldered kits.
If you don't want it to be "connected," try a TemTop P1000. I've torn one apart, and I have it in my office right now - it seems to do what it says on the tin sanely. Temperature, humidity, PM2.5, PM10, and CO2 levels. I have another TemTop unit and they generally agree within some reasonable margin of error, and they do seem to independently measure things like VOC vs CO2 - I can see one rise without the other, depending on what I'm doing.
It doesn't have pressure, though.
https://www.sevarg.net/2021/08/28/temtop-air-quality-sensors...
Indeed! Although it seems the point of the article is that while these are very basic measurements, building the technology to reliably provide correct readings, especially from the same board/housing as a WiFi board, is not trivial. Sure, it's not as difficult as more complex or obscure devices, but it is a lot more than cut & paste some sensors onto a board with some WiFi & slap it in a box... which seems to be the usual level of effort
Does anyone know where we could get such devices that 1) are actually designed to be reliable, and 2) don't need to exfiltrate information to the seller's servers in order for us to access it?
These have worked well for us, they don't do pm2.5 but we have other sensors for that.
There is the AirGradient DIY but I don't like the design, I'm worried about temperature accuracy and response time and I wish it was pluggable into a wall plug.
In addition I want to buy an outdoor water-proof temperature and humidity sensor running on a battery and communicating over WiFi or BT. Also can't find anything.