A security guard or security officer is, usually, a privately-employed person who is employed to protect property and/or people. Usually security guards are uniformed and act to protect property by maintaining a high visibility presence and observing (either directly, through patrols, or by watching alarm systems or video cameras) for signs of crime, fire or disorder; then taking action and/or reporting any incidents to their client, employer and emergency services as appropriate.

The security officer motto is to "detect, deter, observe and report." Security officers are not normally required to make arrests (but has the authority to make a citizens arrest) or otherwise act as police officers except in some United States jurisdictions in which the security officer is invested with arrest powers like those of a county sheriff. In contrast to the above mentioned motto, a Private Security Officer's actual primary duty is prevention of crime. Security personnel do enforce company 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 perform arrests, operate emergency equipment, perform first aid, CPR, take accurate notes and write effective reports, and perform other tasks as required by the property they are protecting. In case of Armed Security Officers who are also called Private Police Officers , are required to go through additional training mandated by the state for carrying weapons such as baton , firearms , handcuffing , arrest and control and pepper spray trainings .

One major economic justification for security guards 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 a security guard 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 guards (particularly in combination with effective security procedures) tends to diminish "shrinkage," theft, employee misconduct and safety rule violations, property damage, or even sabotage. Many casinos hire security guards to protect the money when transferring it from the casino to the casino's bank.

Security officers also perform access control at building entrances and vehicle gates by ensuring that employees and visitors display proper passes or identification before entering the facility. 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 and documenting what happened on an incident report. In case of armed security officers, often they are required to respond like police officers until situation is under control and / or proper authorities arrive on the scene.

Although security officers are a distinct type of personnel from either police officers or the military, in the United States a very high proportion of security personnel, including most senior management personnel, are either former or retired members of one or both services. Many security officers who don't fit this profile (young people in particular) use the job as a springboard into a police career.

Being a private security officer is by no means a lucrative endeavor. Most first line private security personal are paid a low wage which often does not reflect the risks they endure on the job.

Security officers are classified as either of the following
"In-house" or "proprietary" (i.e. employed by the same company or organization they protect, such as a mall, theme park, or casino)
"Contract,? (working for a private security company which protects many locations.)
"Public security" or security police
"Private Patrol Officers" , Patrol gated communities. i.e. Bel-Air Patrol
"Private Police Officers?, also known as Armed Security Officers

Industry terms for various security personnel include: Security , guards, agents, watchmen, officers, safety patrol , Armed Security , Private Police ,Loss Prevention Officers , Bodyguards , Executive Protection Officers . Other job titles in the security industry include dispatcher, receptionist, driver, supervisor, alarm responder, armed security officer, and manager.

Newer terms have been developing within the American security industry that tend to reclassify security personnel into three basic classes, as follows:
Security guards: These personnel, usually uniformed, are primarily responsible for the protection of property only and do not have a responsibility for anything other than basic visibility and reporting. Examples of security guards include night watchmen on construction sites, bank vault guards, and monetary transport guards of money and valuables.

Security officers: These personnel, also usually uniformed, are employed in functions that involve the protection of lives, property and the public peace on private property. Examples of security officers include apartment complex security officers, mall security officers, private patrol officers, and any security personnel that operate in an environment that includes a contractual obligation for the protection of lives and/or the public peace.

Security agents: These personnel, usually without a uniform, are primarily contracted or employed with a focus on apprehension rather than prevention on private property. Examples of security agents include loss prevention agents and personal protection agents (bodyguards).

Security personnel are not police officers but are often confused with them due to similar uniforms and behaviors, especially on private property. Security personnel 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 freedom of an absence of probable cause requirements that frequently dog public law enforcement officers. Additionally, as legal precedents have further restrained the traditional police officers' power of "officer discretion" regarding arrests in the field, requiring a police officer to arrest minor lawbreakers, private security personnel still enjoy such powers of discretion largely due to their private citizen status. Since the laws regarding the limitations of powers generally have to do with public law enforcement, private security is relatively free to utilize non-traditional means to protect and serve their clients' interests. 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.