You've plugged in your carbon monoxide detectors and smoke alarms. You try to use the least toxic cleaning products available, and you've painted your house with non-toxic paint. To the naked eye, you've got the safest possible home. But some toxins are a little harder to spot.

The Environmental Protection Agency had designated January as Radon Action Month, and now is as good a time as any to check to see if this colorless, odorless, radioactive gas is building up in your house.

Radon gas enters a home through cracks in the foundation, holes or cavities around pipes, through floor drains or sump pump openings. Breathing it in creates no immediate symptoms, but over time, it can cause lung cancer, and will significantly increase the risk of lung cancer among smokers who are also exposed to radon. More than 20,000 people will die this year after breathing too much radon without knowing it.

The American Association of Poison Control Centers offers the following tips to protect from radon exposure.

• The only way to figure out if your home has high levels of radon is to perform a test. There are two types of tests: short and long-term.

• Start with a short-term test kit, which can be performed in two to 90 days. You can buy one for anywhere between $5 and $15 at your local hardware store or retailer. These tests typically work by sitting on an out-of-the-way location and absorbing or tracking radon. When the testing period is over, these tests are typically mailed to a laboratory for analysis.

• Long-term tests take at least three months, but tend to be more accurate. Perform these or hire a specialist to perform them if you aren't comfortable with the results of the short-term kit.

• For the do-it-yourself tests, follow the instructions carefully on the packaging. Test the lowest livable area in your home a basement will suffice.

• Test also during the winter months. This provides more accurate results because it's the period of the year when a house is closed up, with no windows open to let radon out.

• If the level is above four picocuries per liter, take action.

• If you do find you have radon, contact your state health department. Most states maintain lists of qualified professionals who can install systems and take steps to keep radon out of your home.

• Fixes could include sealing cracks and gaps and installing a mitigation system that uses ductwork and sometimes a fan to suck the gas out of the basement and out of the home.

• Call your state and local health department to see if they have a radon program. Before you hire a contractor to fix it, they may have recommendations to help.