Security systems can be classified by type of production enterprises, such as industrial, retail (commercial), governmental, government contractor, or hospital; by type of organization, such as contract security or proprietary; by type of security processes, such as personnel or physical security; or by type of security function or emphasis, such as plant protection (variously defined), theft control, fire protection, accident prevention, protection of sensitive (national security or business proprietary) information. Some of these categories obviously overlap.
Security for small businesses constitutes a special situation. Because small firms cannot afford specialized proprietary security staff, measures must be incorporated into regular routines and staff training or be purchased from outside organizations. Theft, both internal and external, is a prime concern.
Residential security constitutes another special category. Sizable housing or apartment complexes, especially if under one management, can employ sophisticated security measures, including, for example, closed-circuit television monitoring of elevators and hallways and trained security guards. Relatively simple equipment for houses or small apartment buildings, as, for example, exterior lighting and alarms, is increasingly used. Some neighbourhoods of large cities cooperatively employ patrol services or organize resident volunteer patrols.
Source: Britannica
