During his 15 years in the South Bronx, Nilo Montalvo says, he has lived in a neighborhood behind bars: vertical rods, child guards, wrought-iron fencing — all wedged into the windows of ground-floor apartments, like his, in a housing project on East 144th Street. “You feel like you’re in prison,” Mr. Montalvo, 64, said.

Recently, though, he has started to notice a change. Some of the steel is gone. Tenants cook with their windows open and unguarded. They read at their computers, near enough for passers-by to touch.

Across neighborhoods long fortified against their own gritty reputations, steel and iron window guards, those often unsightly symbols of the bad old days, have slowly been receding from the city. Once a reliable visual marker of neighborhood borders — no guards, some surmised, implied there was no need for guards — many bars have been casualties of an aesthetics-driven calculation, as families brush aside what they view as outdated home safety concerns.

Joanne Vega, 48, said her family’s longtime home, a ground-floor apartment on Maujer Street in East Williamsburg, Brooklyn, always had window bars in her youth. Recently, though, the steel was removed, Ms. Vega said. “My sister has a German shepherd,” she reasoned.