Health officials are warning Connecticut residents to get in the know if their home has high levels of radon.

Radon is a radioactive gas that is the leading cause of lung cancer. It is invisible, odorless and can be found in soil, rocks and water.

Health officials are urging people to use test kits to detect possible levels of radon in their homes as part of National Radon Action Month.

Radon can leak into homes and other buildings through cracks and foundation openings. 

"Certainly in the winter months, your home is closed with the heating season with the cold weather. This gas, if it does enter the home, it's dangerous," says Thomas Closter, of the Norwalk Health Department. "It's in the area that you're living. You're breathing it in."

On Jan. 8 and 10 from 11 a.m. to 1 p.m., the Norwalk Health Department will be giving out free radon test kits to the first 100 residents who claim them. For those outside of Norwalk, test kits can be bought online or at hardware stores.