No one had yet heard of a Florida teenager named Trayvon Martin when a group of Wisconsin Republicans got together last year to discuss expanding a self-defense bill before the State Legislature.

The bill, known as the Castle Doctrine, made it harder to prosecute or sue people who used deadly force against intruders inside their houses. But the Wisconsin legislators, urged on by the National Rifle Association in a series of meetings, wanted it to go further. They shaped an amendment that extended the bill’s protections to include lawns, sidewalks and swimming pools outside the residences, as well as vehicles and places of business.

That expanded bill, passed with little debate by the Legislature and signed in December by Gov. Scott Walker, a Republican, is the newest of more than two dozen so-called Stand Your Ground statutes that have been enacted around the country in recent years. Those laws are now coming under increased scrutiny after Mr. Martin was shot to death by George Zimmerman, a neighborhood watch coordinator, in late February. Similar legislation is pending in several other states, including Alaska, Massachusetts and New York.

Though the laws vary in their specifics and scope, they expand beyond the home the places where a person does not have a duty to retreat when threatened, and they increase protection from criminal prosecution and civil liability. All contain elements of the 2005 Florida statute that made it difficult to immediately arrest Mr. Zimmerman, who has said he shot Mr. Martin, who was unarmed, in self-defense.