An intrusion detection system, or security alarm is a system designed to detect unauthorized entry into a building or area. Security alarms are used in residential, commercial, industrial, and military properties for protection against theft or property damage, as well as personal protection against intruders.
Intrusion detection systems can also be combined with closed-circuit television surveillance 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 alarms to complicated, multi-area systems with computer monitoring and control.
The most basic alarm consists of one or more sensors to detect intruders, and an alerting device to indicate the intrusion. However, a typical premises security alarm employs the following components:
- 1. Premises Control Unit or Panel is the brains of the system. It reads sensor inputs, tracks arm/disarm status and signals intrusions.
- 2. Sensors are devices which detect intrusions. Sensors are normally placed at the perimeter of the protected area and within it. Sensors detect intruders utilizing a variety of methods including monitoring doors and windows for opening or by monitoring unoccupied interiors for motions, sound, vibration, heat signature or other disturbances.
- 3. Alerting Devices indicate an alarm condition; most commonly these are bells, sirens, and flashing lights. Alerting devices serve the dual purposes of warning occupants of intrusion, and potentially scaring off burglars.
- 4. Keypads are small wall-mounted devices, which function as the human interface to the system. In addition to buttons, keypads typically feature indicator lights and a small display screen.
A basic Instruction Detection System could employ the following types of sensors or detectors:
Passive Infrared: PIR motion detector is one of the most common sensors found in small business environments. It offers affordable and reliable functionality. The term passive refers to the fact that the detector does not generate or radiate its own energy; it works entirely by detecting the heat energy given off by other objects.
Photoelectric Beam: detect the presence of an intruder by transmitting visible or infrared light beams across an area, where these beams may be obstructed. The beams are often employed in stacks of two or more. The technology can be an effective long-range detection system. Systems are available for both internal and external applications.
Glass Break Detectors: may be use for internal perimeter building protection. Glass break acoustic detectors are mounted in close proximity to the glass panes and listen for sound frequencies associated with glass breaking.
Vibration Sensor: mounted on barriers and are used primarily to detect an attack on the structure itself. When movement or vibration occurs, the unstable portion of the circuit moves and breaks the current flow, which produces an alarm. The technology of the devices varies and can be sensitive to different levels of vibration.
Microwave Detectors: emits microwaves from a transmitter and detects any reflected microwaves or reduction in beam intensity using a receiver. The transmitter and receiver are usually combined inside a single housing for indoor applications, and separate housings for outdoor applications.
Ultrasonic Detectors: operates by the transmitter emitting an ultrasonic signal into the area to be protected. The sound waves are reflected by solid objects and then detected by the receiver. Ultrasonic waves are transmitted through air; hard-surfaced objects reflect most of the ultrasonic energy while soft surfaces tend to absorb most of the energy.
In addition to the system itself, security alarms are often coupled with a monitoring service. In the event of an alarm, the premises control unit contacts a central monitoring station. Operators at the station see the signal and take appropriate action, such as contacting property owners, notifying police, or dispatching private security forces. Such signals may be transmitted via dedicated alarm circuits, telephone lines or Internet.