A security guard is a private person who is employed to protect property and people. Usually security guards are uniformed and act to protect property by observing (either directly, through patrols, or by watching alarm systems or video cameras) for signs of crime, fire or disorder; then reporting any incidents to their client, employer and emergency services as appropriate. Security guards 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 guards 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.
The security guard motto is to "observe and report." Contrary to popular belief, security guards are not normally expected to make arrests or otherwise act as police officers. However, security guards do enforce company rules and can act (as would any other person) if necessary to protect lives or property. Security guards are often trained to operate emergency equipment, perform first aid, take accurate notes and write effective reports, and perform other tasks as required by the property they are protecting.
Security guards are either "in-house" (i.e. employed by the same company they protect) or "contract," working for a private security company which protects many locations. Some large private security companies in the USA include Pinkerton, Burns, Wackenhut, Allied, and Guardsmark.
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. This is because having a security guard on site increases the odds that any fire will be 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, or even sabotage.
Most U.S. states and countries require a license to work as a security guard. This license may include a criminal background check and/or training requirements. Most security guards do not carry weapons and have only the same powers of arrest as a private citizen, a "private person" arrest or "citizen's arrest." If weapons are carried, additional permits and training are usually required. Normally armed security guards are used (in the USA) to protect sensitive sites such as government and military installations, banks or other financial institutions, and nuclear power plants. Armed private security is much more rare in Europe and other developed countries. In developing countries (with host country permission) armed security composed mostly of ex-military personnel is often used to protect corporate assets, particularly in war-torn regions.
Some jurisdictions do commission or deputize security guards and give them limited additional powers, particularly when employed in protecting public property such as mass transit stations. Some security guards, particularly in hazardous jobs such as bodyguard work and bouncers outside nightclubs, are off-duty police officers. Except in these special cases, a security guard who misrepresents themselves as police is committing a felony crime.
Industry terms for security guards include: guards, agents, watchmen, officers, safety patrol. Other job titles in the security industry include dispatcher, receptionist, driver, supervisor, alarm responder, armed security officer, and manager.
Derogatory terms for security guards include rent-a-cops and imitation bacon. Some people do not like security guards because their duties include enforcing rules and serving as a symbol of authority. Others believe that security guards are "wanna-be" or would-be police officers, or have had bad experiences with security guards in the past.
References: http://www.dca.ca.gov/bsis/ California. Department of Consumer Affairs, Bureau of Security and Investigative Services Website.