A security officer is usually a privately and formally employed person who is paid to protect property, assets, or people. Security officers are uniformed and act to protect property by maintaining a high visibility presence to deter illegal and inappropriate actions, observing (either directly, through patrols, or by watching alarm systems or video cameras) for signs of crime, fire or disorder; then taking action and reporting any incidents to their client and emergency services as appropriate.

One major economic justification for security personnel is that insurance companies (particularly fire insurance carriers) will give substantial rate discounts to sites which have a 24-hour presence; for a high risk or high value venue, the discount can often exceed the money being spent on its security program. This is because having security on site increases the odds that any fire will be noticed and reported to the local fire department before a total loss occurs. Also, the presence of security personnel (particularly in combination with effective security procedures) tends to diminish theft, safety rule violations, property damage, or even vandalism.

Many security firms and proprietary security departments practice the "detect, deter, observe and report" methodology. Security officers are not authorized to make arrests but may act as an agent of law enforcement at the request of a police officer, sheriff, and others in the event of an emergency.

In addition to the methodology mentioned above, a private security officer's primary duty is the prevention and deterrence of crime. Security personnel enforce rules and can act to protect lives and property. In fact, they frequently have a contractual obligation to provide these actions. Security officers are often trained to operate emergency equipment, perform first aid, CPR, take accurate notes, write detailed reports, and perform other tasks as required by the contractee they are serving. Positions are also set to grow in the U.S., with 350,000 new security jobs expected over the next decade.

Security personnel may also perform access control at building entrances and vehicle gates; meaning, they ensure that residents, employees and visitors display proper passes or identification before entering the property. Security officers are often called upon to respond to minor emergencies (lost persons, lockouts, dead vehicle batteries, etc.) and to assist in serious emergencies by guiding emergency responders to the scene of the incident, helping to redirect foot traffic to safe locations, and by documenting what happened on an incident report.

Patrolling is usually a large part of a security officer's duties. Often these patrols are logged by use of a guard tour patrol system, which require regular patrols. Although security officers differ greatly from police officers, military personnel, federal agents/officers, and the like, the United States has a growing proportion of security personnel that have former police or military experience, including senior management personnel. On the other hand, some security officers, young people in particular, use the job as practical experience to use in applying to law enforcement agencies.

Industry terms for various security personnel include: Security guards, security agents, watchmen, security officers, safety patrol, Armed Security, Private Police, Company police, Loss Prevention, Bodyguards, Executive Protection Agents, or Access Managers. Other job titles in the security industry include dispatcher, receptionist, driver, supervisor, alarm responder, mall security officer, private patrol officer, Private Patrol Operator, and manager.

There is a marked difference between persons performing the duties historically associated with watchmen and persons who take a more active role in protecting persons and property. The former, often called "guards," are taught the mantra "observe and report," are minimally trained, and not expected to deal with the public or confront criminals. The latter are often highly trained, sometimes armed depending on contracts agreed upon with clientele, and are more likely to interact with the general public and to confront the criminal element. These employees tend to take pride in the title "Security Officer" or "Protection Officer" and disdain the label of "guard." Ironically enough, there may be no relationship between duties performed and compensation -- many mall "security officers" who are exposed to serious risks make less per hour than "industrial security guards" with less training and responsibility. However, there are now more positions in the security role that separate not just the titles, but the job itself. The roles have progressed and so have the areas for which security people are needed. All security jobs vary in pay and duties at present.

Security personnel are essentially private citizens, and therefore are bound by the same laws and regulations as the citizenry they are contracted to serve, and therefore are not allowed to represent themselves as law enforcement under penalty of law.

Security personnel are not police officers, but are often identified as such due to similar uniforms and behaviors, especially on private property. Security personnel in the U.S. derive their powers not from the state, as public police officers do, but from a contractual arrangement that give them 'Agent of the Owner' powers. This includes a nearly unlimited power to question with the absence of probable cause requirements that frequently limit public law enforcement officers, provided that the security officer does not tread on the rights and liberties of others as guaranteed by the United States Constitution. This does not come without checks, however, as private security personnel do not enjoy the benefit of civil protection, as public law enforcement officers do, and can be sued directly for false arrests and illegal actions if they commit such acts.

Sometimes police officers work as security personnel while not on duty. This is usually done for extra income; the work they do comes with their training and law enforcement experience and is a great asset to the company they work for as well and the clients they serve.

Security personnel who misrepresent themselves as police officers are committing a crime. However, security personnel by their very nature often work in cooperation with police officials. Police are called in when a situation warrants a higher degree of authority to act upon reported observations that could not be directly acted upon safely by the security personnel.