CHICAGO (CBS) — Radon is an invisible threat lurking in thousands of Illinois homes.

The CBS 2 Morning Insiders have dug into state records and have found that alarming radon levels showed up in 80,000 Illinois homes just since 2015. As CBS 2’s Tim McNicholas pointed out, it is a leading cause of lung cancer.

A low whirr can be heard outside Barbara Sorgatz’s house – coming from a black box mounted to the outside wall. It might just be the sound of a healthy home.

“It pumps radon out of my house,” Sorgatz explained.

The system sends radon through pipes and out of the house. She has had the system in operation since 2007.

“At least six or seven homes just on this block have had radon systems installed because of my story,” Sorgatz said.

Her story starts in 2006, when she was diagnosed with lung cancer. She learned radon is the leading cause of lung cancer for non-smokers like her.

So she had her home tested and found radon levels up to five times the Environmental Protection Agency safety threshold.

“My word is to have everyone test their home for radon,” Sorgatz said. “The test kits are very inexpensive.”

She beat the cancer, and now she warns others about the invisible byproduct of uranium that forms in the soil under homes.

CBS 2 requested data from the Illinois Emergency Management Agency and found that more than 80,000 Illinois homes have tested with high radon levels since 2015.

“That’s 80,000 of the homes that have been tested,” Sorgatz said. “Imagine all the ones that haven’t been tested. That’s a lot of homes.”

The law says landlords need to tell renters whether a test has been conducted, but they don’t have to test. Sellers are also required to tell a buyer if the home’s been tested, but again, a test is not legally required.

Sorgatz had to have part of her lung removed. Sher doesn’t want anyone else to go through that.

Sorgatz is reminding people that January is National Radon Month, and you can pick up a testing kit at your local hardware store and monitor your indoor air quality with detectors from AirThings.

Tim McNicholas