MILWAUKEE – The neighborhood rocked by violent protests after a black officer fatally shot a black man was calmer after police pledged to strictly enforce a curfew for teenagers in Milwaukee, the latest place where authorities have invoked decades-old, often little-enforced laws to try to tamp down unrest.

But the measures are controversial, with some people saying curfews violate civil liberties. Researchers argue there’s little to no evidence the laws work, particularly when it comes to curbing juvenile crime. And in some cases, they say, the laws only make problems worse.

“The most useful aspect of a curfew is it gives the public an impression that the police are doing something,” said Kenneth Adams, a criminal justice professor at the University of Central Florida. “It’s sending the message that ‘We the police are serious about restoring order, and we’re going to take steps.’”

Authorities in Ferguson, Missouri, issued curfews for all residents in 2014 in response to violence that erupted after a white officer shot and killed a black 18-year-old, a move that angered many in the community.

Milwaukee’s enforcement was aimed at teens and followed riots that started after the Saturday shooting of Sylville Smith. Police say the 23-year-old was fleeing a traffic stop and had a gun in his hand when he turned toward the officer, who opened fire.

Peaceful protests turned violent that night and continued Sunday evening. Some businesses were set on fire, one person was shot and multiple officers were injured.

Milwaukee has had a curfew law on its books since 1943. It prohibits people under age 17 from loitering in public places between 11 p.m. and 5 a.m. during the summer, and from 10 p.m. to 5 a.m. Sunday through Thursday during the school year.

The proclamation Mayor Tom Barrett issued Monday expanded the curfew to apply to anyone under 18. It also took effect an hour earlier, at 10 p.m.

“Your teenagers better be home or in a place where they’re off the streets,” he said Monday.

Police said that night was markedly more peaceful.