“My family would be here had I known that weather radios existed,” said Kathryn Martin, who pushed heavily for the law after the tornado shattered the Eastbrook Mobile Home Park and killed dozens of people, including three of her relatives.

The Indiana regulation is one of hundreds of new laws taking effect on July 1, when most states begin their fiscal years. Among them are efforts to encourage alternative energy in Nevada and Minnesota, tougher rules against illegal immigrants in Georgia and Idaho, and higher minimum wages in Illinois, Michigan and Pennsylvania.

The Indiana tornado hit before dawn on Nov. 6, 2005, with winds estimated at 200 miles an hour. Twenty of the 25 victims of the storm were in mobile homes on the outskirts of Evansville, where emergency officials said few had radios or access to shelters.

The Indiana General Assembly responded last year, passing the weather-radio proposal with overwhelming support. A similar effort is under way on the federal level to make the radios a requirement nationwide.

The radios, which cost about $30, operate on frequencies dedicated to the weather service. Officials say they often broadcast warnings before regular radio and television stations.

More than 20 million Americans live in mobile homes, according to Census estimates. The National Oceanic and Atmospheric Administration has found that the fatality rate for residents of mobile homes is 10 times greater than those in homes with fixed foundations.

These are among other laws taking effect on July 1:

- Virginia will require convicted sex offenders to register e-mail addresses with the state.

- Nevada will force certain sex offenders to live at least 1,000 feet from schools and other places where children gather.

- Tennessee will require everyone buying beer at a store to show ID.

- California will ban sales of soda in schools during school hours and put new limits on sugar and fat content in school food.

- Colorado will ban abstinence-only sex education in all schools, except for one district, requiring schools to teach sex education based on scientific research and to include information on contraception.

In Indiana, people riding in back seats and in S.U.V.’s and pickups will have to wear seat belts. The mandatory belt law had a loophole for vehicles with truck plates.