I guess it takes legal requirements for the landlord to do what's right

You can buy an active monitor like a carbon monoxide detector for around $100. And the levels can fluctuate wildly in my personal limited experience

Ventilate as often as possible.

I am measuring radiation in certain areas in my basement where I am renting, in the iving room and kithcen junction, with strong hummeing comming from the ceiling. It happens in the night time. I am using frequency meter and the meter measuring high levels of radiation in that junction. It is also accompanies with slight headache. What that could be? It also seem to interfere with the Wifi. This is weired.