Some alarm systems serve a single purpose of burglary protection; combination systems provide both fire and intrusion protection. Intrusion alarm systems may also be combined with closed-circuit television surveillance (CCTV) systems to automatically record the activities of intruders, and may interface to access control systems for electrically locked doors.

Systems range from small, self-contained noisemakers, to complicated, multi-rally systems with computer monitoring and control. It may even include two-way voice which allows communication between the panel and Monitoring station.

Closed-circuit television (CCTV), also known as video surveillance,  is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors. It differs from broadcast television in that the signal is not openly transmitted, though it may employ point-to-point (P2P), point-to-multipoint (P2MP), or mesh wired or wireless links. Though almost all video cameras fit this definition, the term is most often applied to those used for surveillance in areas that require additional security or ongoing monitoring. Though videotelephony is seldom called “CCTV” one exception is the use of video in distance education, where it is an important tool.

Surveillance of the public using CCTV is common in many areas around the world. In recent years, the use of body worn video cameras has been introduced as a new form of surveillance, often used in law enforcement, with cameras located on a police officer’s chest or head.  Video surveillance has generated significant debate about balancing its use with individuals’ right to privacy even when in public.

In industrial plants, CCTV equipment may be used to observe parts of a process from a central control room, for example when the environment is not suitable for humans. CCTV systems may operate continuously or only as required to monitor a particular event. A more advanced form of CCTV, using digital video recorders (DVRs), provides recording for possibly many years, with a variety of quality and performance options and extra features (such as motion detection and email alerts).

More recently, decentralized IP cameras, perhaps equipped with megapixel sensors, support recording directly to network-attached storage devices, or internal flash for completely stand-alone operation.

By one estimate, there will be approximately 1 billion surveillance cameras in-use worldwide by 2021.  About 65% of these cameras are installed in Asia. The growth of CCTV has been slowing in recent years. The deployment of this technology has facilitated a significant growth in state surveillance, a substantial rise in the methods of advanced social monitoring and control, and a host of crime prevention measures throughout the world.