No Stupid Questions

Those are almost certainly wired to a central alarm panel that will trigger alarms throughout the building if you test them yourself.

Talk to your property manager about your concerns. It's their responsibility to maintain and test yearly.

I used to calibrate industrial gas detectors. They generally have an active air sampling path with a pump and a sensor in the gas flow path, and we would calibrate them by flooding the sensor chamber with a test gas at a known concentration. For the type of sensor you have none of those conditions exist (no controlled gas flow path and no pump) so there is essentially no way you can accurately test their response. You essentially have to trust the manufacturer to have made a good product. The one thing you can do is look for an install date and (hopefully) an expiration date, if you can inspect the back of the detector without setting off any central alarm system. If you really don’t trust the owner’s sensors, you can always buy and use your own. Just make sure you place them carefully according to the manufacturer’s instructions.

Also, your detectors are probably combo smoke/CO, but not natural gas. You would smell the odorant in the gas long before the concentration becomes dangerous so a detector would be redundant.

Honestly just buy your own detectors. Then you are double protected.

Working parallel to that industry, those likely are just smoke detectors. CO2 typically you want low down close to the floor. I any seen gas detectors in motorhomes but also been low to the floor.

I don't know what the building codes / rules are where you live, but where I live (in the US), there is supposed to be a smoke detector in every bedroom. Newer code also requires them to be hardwired so 1) no batteries to change and 2) if one goes off, they all go off.

I put kiddie z-wave enabled smoke/CO detectors throughout the house, including one in every bedroom. They are linked into a monitored alarm system (abode), but that is mainly for keeping track of things when we are not at the house, and I m going to eventually switch to home assistant.

Since the main ones are already wired in, you could probably add at least the dumb smoke and CO detectors to every room for extra peace of mind.

Smoke? Burn something. Gas? Hold an unignited lighter up to it. CO? Burn something in a low oxygen environment next to it :)

This stuff is important, take it from someone who had headaches for months before concentrations tripped a CO alarm and I found a blocked flue. CO detectors should be trustworthy, they just don't trip below 100ppm@90 minutes. Just make sure to replace them every 10 years. You can get a separate CO alarm from Kidde that will read out concentrations below trip point, or you can splurge for various CO sensors available. I recall seeing some Z-Wave ones that test for various indoor pollutants.