Security guards 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

Industry terms for various security personnel 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.

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).

Licensing

Most U.S. states and counties 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 the same powers of arrest as a private citizen, called a "private person" arrest, "any 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. However, armed security is quickly becoming a standard for vehicle patrol officers and on many other non-government sites. Armed private security is much rarer in Europe and other developed countries (and unknown in some, such as the United Kingdom). 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.

Security guards and the police

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.

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. This is a special case that is often unique to a particular jurisdiction or locale.

Some security officers with police powers, typically employed directly by governmental agencies, are called security police. Typically these are police whose duties primarily involve the security of a government installation, and are also a special case.

Some security guards, particularly in hazardous jobs such as bodyguard work and bouncers outside nightclubs, are off-duty police officers (although in some countries, including the United Kingdom, it is illegal for police officers to take private security work).

Except in these special cases, a security guard who misrepresents himself as a police officer is 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 of the security personnel that could not be directly acted upon safely by the security personnel.