Radon can't be seen, smelled, or tasted. It is dangerous because it is radioactive and it can cause lung cancer.
It enters your house because the air pressure in your house is usually lower than the pressure in the soil around your house’s foundation which acts like a vacuum drawing radon through the cracks in the foundation and other openings.
Getting a radon tester is easy and doesn't cost as much as you think. A radon tester can cost as little as 10 dollars. If you test your house and you have radon you can get it out of your house by having getting an Active Sub-slab suction.