A security guard, (or security officer) is usually a privately and formally employed person who is paid to protect property, assets, or people.

Often, 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.

Functions and duties

Many security firms and proprietary security departments practice the "detect, deter, observe and report" methodology. Security officers are not required to make arrests, but have the authority to make a citizen's arrest, or otherwise act as an agent of law enforcement at the request of a police officer, sheriff, and others.
In addition to the methodology mentioned above, a private security officer's primary duty is the prevention and deterrence of crime. Security personnel 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 arrest and control procedures (including handcuffing and restraints), 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.

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 "shrinkage," theft, employee misconduct and safety rule violations, property damage, or even sabotage. Many casinos hire security guards to protect money when transferring it from the casino to the casino's bank.

Security personnel may also perform access control at building entrances and vehicle gates; meaning, they ensure 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, helping to redirect foot traffic to safe locations, and by documenting what happened on an incident report.