Your fire alarms most likely have a CO detector, not a CO2 detector. I don’t really know the point of a CO2 detector, though, so I agree with you on everything. Just get a few more indoor plants if CO2 is a concern.

Maybe decades ago, but not now.

This is definitely a question for HR, but generally an employment change is a “life event”.

I started with Ubuntu back when you could put in your parent’s home address and they sent you free CDs. I’m on Arch (since about 2010), and I can’t change.