They range from guards in toy stores and parking lots to experts in corporate counterespionage. Some wear uniforms and carry guns, others dress in plainclothes and use sophisticated laboratories.
Together, they make up a private security force that is now twice the size of all the public police forces in the United States.
Americans who can afford it have stopped relying on the government to protect them from crime. They are hiring their own police.
"People are really frightened," said James K. Stewart, former head of the National Institute of Justice, the Justice Department's think tank.
"And at the same time, there's diminishing confidence in the criminal justice system's ability to provide comfort and safety," he said.
National spending on alarm and surveillance systems, private guards and investigators -- the whole panoply of purchased protection -- soared to $52 billion last year. That's more than 2 1/2 times what the industry spent in 1980.
It's also far more than the approximately $30 billion spent last year on police protection by federal, state and local governments.
These numbers tell of more than fear and frustration. To Mr. Stewart and others, they suggest that something fundamental is changing. More and more, people are buying small swaths of safety in an environment that feels increasingly dangerous.
The result could be a two-tier system -- with one brand of safety for the rich and another, cheaper version for the poor.
And if society splits that way, something central to the American ideals of equality and justice could be fractured as well.
"Something has really changed in this country," said Mr. Stewart, now a consultant in Maryland. "I'd say we are moving from a system of justice to a system where people are purchasing security. Which is different from justice.
"Because justice is a value that benefits all of society. Private security partitions off security to just a few."
Inspector Thomas Seamon of the Philadelphia Police Department puts it this way: "There's a distinct danger that the police could be the police of the poor, and anyone who can afford it will have private security."
An example of this can be found in some private communities in Southern California and Florida, surrounded by 24-hour guard gates and their own roving patrols.
Nearly 1.5 million people are employed in private security, compared with the 600,000 who work in public law enforcement, according to Hallcrest Systems Inc., a research and consulting firm in McLean, Va.
By 2000, "75 percent of protection for our collective society will be done privately," said William C. Cunningham, Hallcrest's president.
"The growth is spectacular," said Ira S. Somerson, a security management consultant based in Plymouth Meeting, Pa., a suburb of Philadelphia.
Mr. Stewart said the boom shows how public confidence in the criminal justice system has fallen. Only one-third of all crimes are reported to police, Mr. Stewart noted -- an indication that many people don't trust the system to help them.
He said that prison crowding has put many criminals back on the streets and that a "defendants' bias" in the courts discourages many victims from seeking justice.
"The feeling is, I've been attacked, and I don't want to get screwed up more," Mr. Stewart said.
"When I came into policing in 1970, there were 300,000 to 400,000 people in private security, and 500,000 in policing," said Michael Shanahan, chief of the University of Washington's police department.
"So we [in law enforcement] were much bigger -- and we've watched them grow and grow and grow," he said.
Installations of home burglar alarms rose 10 percent last year, compared with 2 percent in 1980. The devices are so plentiful that police spend about one-quarter of their time responding to false alarms, according to Simon Hakim, an economics professor at Temple University in Philadelphia.
The surge in private protection coincides with a decline in many city budgets. Local governments increasingly are unable to provide traditional levels of service. As they founder, private prisons, private crime watches, even the private resolution of disputes out of court are on the rise.
In some respects, the trend is a case of American history coming full circle. The first public police force was not founded until 1844, in New York City. In colonial days, law was enforced by constables and a night watch made up of citizens who took turns on the lookout for fires and the unruly.
By the 1800s, most people who could afford it paid for someone else to take their watch.
Benjamin Franklin wrote in his diaries that the watches were one of the biggest problems of a municipal executive. The paid watchmen were often drunk and their watches unreliable.
"In many ways, the security industry is an American-original industry," said Robert McCrie, editor of Security Letter, an industry newsletter. "Such commercial businesses as guarding, investigating, alarms, armored-guard services have all been created in the United States in the 19th century."
Today's challenge is to get private forces -- often without power to make arrests, and rarely armed -- to cooperate with public police.
"If we can develop a synergy so we work at joint purposes, the public can benefit," said the University of Washington's Mr. Shanahan, who heads a task force on private security issues for the International Association of Chiefs of Police.
"We've got to make sure we've got some common bonds," Mr. Shanahan said, "so we don't have safety in America based on your ability to pay for safety."