Bulletproof vests have saved the lives of many police officers caught in the line of fire, but cops in some departments aren't required to wear them.
The federal government is pushing to make the vests mandatory, using grants to local law enforcement as an incentive.
More than 3,000 officers have survived shootings since the mid-1970s thanks to body armor, according to the National Institute of Justice, the research arm of the Department of Justice.
Police are required to wear bullet-resistant vests in Hempstead Village, where an officer survived a shooting early Friday.
The Nassau County Police Department doesn't mandate use of the vests but encourages officers to wear them.
A Suffolk police spokeswoman said officers must wear them on patrol and during enforcement activities.
The New York City Police Department requires only uniformed cops to wear vests.
"I personally wore it every day when I was on the street," said Jim Carver, president of the Nassau County Police Benevolent Association. "It got to a point where I felt naked without the vest."
The vests have evolved to become lighter and more effective since being developed for widespread use after the 1960s. They are made of synthetic fiber that absorbs bullets and disperses the energy of the impact, experts said.
"There are two objectives: one is to stop the bullet; the other is . . . to stop blunt-force trauma," said Mark Smith, vice president of sales for Point Blank Enterprises, a body armor company in Pompano Beach, Fla.
Even with the vests, officers can end up with bruises and broken bones, or suffer heart attacks from the hits, Smith said.
The Justice Department last year began requiring that police departments receiving federal body armor grants have policies mandating use of the vests.
A 2009 Justice report cited a national survey that found only 59 percent of law enforcement agencies require officers to wear body armor at least some of the time.
Police associations prefer giving officers the discretion to avoid carrying the extra bulk if they're not on patrol.
"These vests are lifesavers, no doubt about it," said William J. Johnson, of the National Association of Police Organizations in Alexandria, Va.
But he said there are circumstances, such as undercover duty, "where an officer is not able to wear them."
With Matthew Chayes and Anthony M. DeStefano