Alarm system Sensors are connected to a control unit via a low-voltage hardwire or narrowband RF signal which is used to interact with a response device. Burglar alarms are divided to two main fields: home burglar alarms and industrial burglar and perimeter intrusion detection. Home burglar alarms are often systems assembled from inexpensive infrared detectors that the home owner or the security contractor will install in front of all the windows and doors in the house. These infrared sensors are designed for indoor use only and should not be used outside. In the field of industrial security systems, the methodology of protection is quite different. First is to detect, second to delay and third to alarm. Industrial alarm systems are designed as an integration of several sensor systems. The most important for big facilities would be the outer fence on which a sensor is placed. It would detect and delay the intruders before they even reach the building itself. Alarm types Indoor The passive infrared detector (PIR) is one of the most common detectors found in household and small business environments because it offers affordable and reliable functionality.
PIRs are able to distinguish if an infrared emitting object is present by first learning the ambient temperature of the monitored space and then detecting a change in the temperature caused by the presence of an object. Ultrasonic Detectors Using frequencies between 25 kHz and 75 kHz, these active detectors transmit ultrasonic sound waves that are inaudible to humans. The Doppler shift principle is the underlying method of operation, in which a change in frequency is detected due to object motion. This is caused when a moving object changes the frequency of sound waves around it. Microwave Detectors This device emits microwaves from a transmitter and detects microwaves at a receiver, either through reflection or reduction in beam intensity. The transmitter and receiver are usually combined inside a single housing (monostatic) for indoor applications, and separate housings (bistatic) for outdoor applications. Glass Break Detectors The glass break detector may be used for internal perimeter building protection. When glass breaks it generates sound in a wide band of frequencies. These can range from infrasonic, which is below 20 Hertz (Hz) and can not be heard by the human ear, through the audio band from 20 Hz to 20 kHz which humans can hear, right up to ultrasonic, which is above 20 kHz and again cannot be heard. Glass break acoustic detectors are mounted in close proximity to the glass panes and listen for sound frequencies associated with glass breaking. Seismic glass break detectors are different in that they are installed on the glass pane. When glass breaks it produces specific shock frequencies which travel through the glass and often through the window frame and the surrounding walls and ceiling. Outdoor Vibration (Shaker) or Inertia Sensors These simple devices are mounted on barriers and are used primarily to detect an attack on the structure itself. The technology relies on an unstable mechanical configuration that forms part of the electrical circuit. When movement or vibration occurs, the unstable portion of the circuit moves and breaks the current flow, which produces an alarm Fibre Optic Cable A fibre-optic cable can be used to detect intruders by measuring the difference in the amount of light sent through the fibre core. If the cable is disturbed, light will ‘leak’ out and the receiver unit will detect a difference in the amount of light received. The cable can be attached directly to a chainwire fence or bonded into a barbed steel tape that is used to protect the tops of walls and fences. System connections The trigger signal from each sensor is transmitted to one or more control unit(s) either through wires or wireless means (radio, line carrier, infrared). Wired systems are convenient when sensors (such as smoke detectors) require power to operate correctly, however, they may be more costly to install. Alarm connection and monitoring Depending upon the application, the alarm output may be local or remote or a combination. Local alarms do not include monitoring, though may include indoor and/or outdoor sounders (e.g. motorized bell or electronic siren) and lights (e.g. strobe light) which may be useful for signaling an evacuation notice for people during fire alarms, or where one hopes to scare off an amateur burglar quickly. Remote alarm systems are used to connect the control unit to a predetermined monitor of some sort, and they come in many different configurations. High-end systems connect to a central station or responder (eg. Police/ Fire/ Medical) via a direct phone wire (or tamper-resistant fiber optic cable), and the alarm monitoring includes not only the sensors, but also the communication wire itself. Broadband Alarm Monitoring Legacy dial up analogue alarm panels or systems with serial/parallel data ports are normally migrated to broadband by the addition of a Alarm Server device which converts those DTMF tones or RS232/485 data bits to IP. Listen In Alarm monitoring Monitored alarms and speaker phones allow for the central station to speak with the homeowner and/or intruder. This may be beneficial to the owner for medical emergencies. Alarm response Depending upon the zone triggered, number and sequence of zones, time of day, and other factors, the monitoring center can automatically initiate various actions. They might be instructed to call the ambulance, fire department or police department immediately, or to first call the protected premises or property manager to try to determine if the alarm is genuine. | 
