Gov. Jim Doyle has signed a law that will require all homes and duplexes to contain carbon monoxide detectors as a safety precaution.

The law will require detectors on every level of the home, including the basement, but not the attic or storage areas. It takes effect next year.

Supporters say the requirement will save lives even though there is no penalty for not complying. They say up to 2,000 Americans die every year from carbon monoxide poisoning.

The bill enjoyed bipartisan support, but some Republican critics complained it was an unnecessary mandate. The governor signed it in private Wednesday.