Security alarm

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Wireless home alarm system control panel
A house alarm

A security alarm is a system designed to detect intrusion – unauthorized entry – into a building or other area such as a home or school. Security alarms are used in residential, commercial, industrial, and military properties for protection against burglary (theft) or property damage, as well as personal protection against intruders. Security alarms in residential areas show a correlation with decreased theft.[1] Car alarms likewise help protect vehicles and their contents. Prisons also use security systems for control of inmates.

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, multirally systems with computer monitoring and control. It may even include two-way voice which allows communication between the panel and Monitoring station.


Exterior alarm bell box
Alarm CPU panel with inputs and outputs


  • Premises control unit (PCU), alarm control panel (ACP), or simply panel: The "brain" of the system, it reads sensor inputs, tracks arm/disarm status, and signals intrusions. In modern system, this is typically one or more computer circuit boards inside a metal enclosure, along with a power supply.


Sensor types[edit]

Hermetically sealed reed switches[edit]


Passive infrared detectors[edit]

A passive infrared sensor used to detect motion



PIR sensors may be designed to be wall- or ceiling-mounted, and come in various fields of view, from narrow-point detectors to 360-degree fields. PIRs require a power supply in addition to the detection signalling circuit.

Infrasound detectors[edit]

The infrasound detector works by detecting infrasound, or sound waves at frequencies below 20 hertz. Sounds at those frequencies are inaudible to the human ear.[2] Due to its inherent properties, infrasound can travel distances of many hundreds of kilometers. Infrasound signals can result from volcanic eruptions, earthquakes, gravity waves, opening and closing of doors, forcing windows to name a few.[3]

The entire infrasound detection system consists of the following components: a speaker (infrasound sensor) as a microphone input, an order-frequency filter, an analog to digital (A/D) converter, and finally an MCU, which is used to analyse the recorded signal.

Each time a potential intruder tries enter into a house, she or he tests whether it is closed and locked, uses tools on openings, or/and applies pressure, and therefore he or she creates low-frequency sound vibrations. Such actions are immediately detected by the infrasound detector before the intruder breaks in.

The primary purpose of such system is to stop burglars before they enter the house, to avoid not only theft, but vandalism. The sensitivity can be modulated depending on the size of a house and presence of animals.

Ultrasonic detectors[edit]




Microwave detectors[edit]



  • Advantages: low cost, easy to install, invisible perimeter barrier
  • Disadvantages: May be affected by weather conditions like rain, snow and fog. Typically need a sterile clearance area to prevent partial blocking of the detection field.

Compact surveillance radar[edit]


Photoelectric beams[edit]


Glass-break detection[edit]

The glass-break detector may be used 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.


Window foil is a less sophisticated, mostly outdated detection method that involves gluing a thin strip of conducting foil on the inside of the glass and putting low-power electric current through it. Breaking the glass is practically guaranteed to tear the foil and break the circuit.

Smoke, heat, and carbon monoxide detectors[edit]

Most systems may also be equipped with smoke, heat, and/or carbon monoxide detectors. These are also known as 24-hour zones (which are on at all times). Smoke and heat detectors protect from the risk of fire using different detection methods. Carbon monoxide detectors help protect from the risk of carbon monoxide poisoning. Although an intruder alarm panel may also have these detectors connected, it may not meet all the local fire code requirements of a fire alarm system.

Traditional smoke detectors are technically ionisation smoke detectors which create an electric current between two metal plates, which sound an alarm when disrupted by smoke entering the chamber. Ionisation smoke alarms can quickly detect the small amounts of smoke produced by fast-flaming fires, such as cooking fires or those fueled by paper or flammable liquids. A newer, and perhaps safer, type is a photoelectric smoke detector. It contains a light source in a light-sensitive electric sensor, which is positioned at a 90-degree angles to the sensor. Normally, light from the light source shoots straight across and misses the sensor. When smoke enters the chamber, it scatters the light, which then hits the sensor and triggers the alarm. Photoelectric smoke detectors typically respond faster to a fire in its early, smoldering stage – before the source of the fire bursts into flames.

Motion sensors[edit]

Motion sensors are devices that use various forms of technology to detect movement. The technology typically found in motion sensors to trigger an alarm includes infrared, ultrasonic, vibration and contact. Dual technology sensors combine two or more forms of detection in order to reduce false alarms as each method has its advantages and disadvantages. Traditionally motion sensors are an integral part of a home security system. These devices are typically installed to cover a large area as they commonly cover up to 40 ft with a 135° field of vision.

Driveway alarms[edit]

Driveway alarm systems can be tied into most security and automation systems. They are designed to alert residents to unexpected visitors, intruders, or deliveries arriving at the property. They come in magnetic and infrared motion sensing options. Driveway alarms can also be purchased in hard-wired and wireless systems. They are common in rural security systems as well as for commercial applications.

Electro-mechanical (shaker) sensors[edit]

These electro-mechanical 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. The medium transmitting the vibration must be correctly selected for the specific sensor as they are best suited to different types of structures and configurations. This technology is gradually being replaced by intelligent digital accelerometer-based systems.

  • Advantages: Low-cost and easily installed on existing fences.
  • Disadvantages: Must be fence-mounted. Being mechanical in nature, the system is unable to analyze differences in the pattern of vibrations (for example, the difference between gusts of wind and a person climbing the fence).

Ferrous metal detectors[edit]

Change in the local magnetic field due to the presence of ferrous metals induces a current in the buried sensors (buried cables or discrete sensors) which is analyzed by the system. If the change exceeds a predetermined threshold, an alarm is generated.[4] This type of sensor can be used to detect intruders carrying substantial amounts of metal, such as a firearm, making it ideally suited for anti-poaching applications.[5]

Electrostatic field[edit]

Sometimes referred to as E-field, this volumetric sensor uses Electric field proximity sensing and can be installed on buildings, perimeters, fences, and walls. It also has the ability to be installed free-standing on dedicated poles. The system uses an electromagnetic field generator powering one wire, with another sensing wire running parallel to it. The sensing wire is connected to a signal processor that analyses:

  • amplitude change (mass of intruder),
  • rate change (movement of intruder),


The barrier can provide vertical protection from the ground to the height of the mounting posts (typically 4–6 metres of height), depending on the number of sensor wires installed. It is usually configured in zones of about 200 metre lengths.

  • Advantage: High-security (difficult to defeat), high vertical detection field.
  • Disadvantages: Expensive, short zones which mean more electronics (and thus a higher cost).

Microphonic systems[edit]


Microphonic systems vary in design (for example, time-domain reflectrometry or piezo-electric) but each is generally based on the detection of an intruder attempting to cut or climb over a fence. Usually the microphonic detection systems are installed as sensor cables attached to rigid chainwire fences, however some specialised versions of these systems can also be installed as buried systems underground. Depending on the version selected, it can be sensitive to different frequencies or levels of noise or vibration. The system is based on coaxial or electro-magnetic sensor cable with the controller having the ability to differentiate between signals from the cable or chainwire being cut, an intruder climbing the fence, or bad weather conditions.


  • Advantages: Relatively inexpensive compared to other systems and easy to install.
  • Disadvantage: Older systems may have a high rate of false alarms caused by wind and other distances, although newer systems use DSP (digital signal processing) to process the signal and greatly reduce false alarms in some cases.

Taut wire fence systems[edit]

A taut wire perimeter security system is basically an independent screen of tensioned tripwires usually mounted on a fence or wall. Alternatively, the screen can be made so thick that there is no need for a supporting chainwire fence. These systems are designed to detect any physical attempt to penetrate the barrier. Taut wire systems can operate with a variety of switches or detectors that sense movement at each end of the tense wires. These switches or detectors can be a simple mechanical contact, static force transducer or an electronic strain gauge. Unwanted alarms caused by birds and other animals can be avoided by adjusting the sensors to ignore objects that exert small amounts of pressure on the wires. This type of system is vulnerable to intruders digging under the fence. A concrete footing directly below the fence is installed to prevent this type of attack.

  • Advantages: low rate of false alarms, very reliable sensors, and high rate of detection.
  • Disadvantages: very expensive and complicated to install.

Fibre optic cable[edit]

A fibre-optic cable can be used to detect intruders by measuring the difference in the amount of light sent through the fibre core. A variety of fiber optic sensing technologies may be used, including rayleigh scattering or interferometry, If the cable is disturbed, the light will be changed and the intrusion detected. 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. This type of barbed tape provides a good physical deterrent as well as giving an immediate alarm if the tape is cut or severely distorted.

  • Advantages: Being cable-based, very similar to the microphonic system and easy to install.
  • Disadvantage: Typically performs in a manner similar to microphonic-based systems but at a higher cost and complexity due to the use of fiber optic technology.

Ported coaxial cable[edit]

Ported coaxial cable installation.png

This system employs an electro-magnetic field disturbance principle based on two unshielded (or 'leaky') coaxial cables buried approximately 30 cm (1 ft) deep and 1 m (3 ft) apart.[6] The transmitter emits continuous Radio Frequency (RF) energy along one cable and the energy is received by the other cable. When the change in field strength weakens due to the presence of an object and reaches a pre-set lower threshold, an alarm condition is generated. The system is covert after installation. Care must be taken to ensure the surrounding soil offers good drainage in order to avoid nuisance alarms.

  • Advantage: concealed as a buried form.
  • Disadvantages: can be affected by RF noise, difficult to install.

Security electric fence[edit]



  • Disadvantage: potential for unintended shock.

Wired, wireless, and hybrid systems[edit]

Installing a wireless magnetic contact breaker on a door

The trigger signal from every 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 PIRs, smoke detectors, etc.) require external power to operate correctly; however, they may be more costly to install. Entry-level wired systems utilize a star network topology, where the panel is at the center logically, and all devices home run their line wires back to the panel. More complex panels use a Bus network topology where the wire basically is a data loop around the perimeter of the facility, and has drops for the sensor devices which must include a unique device identifier integrated into the sensor device itself (e.g. id. biscuit). Wired systems also have the advantage, if wired properly for example by dual loop, of being tamper-evident.

Wireless systems, on the other hand, often use battery-powered transmitters which are easier to install and have less expensive start-up costs, but may fail if the batteries are not maintained. Depending on distance and construction materials, one or more wireless repeaters may be required to bring the signal to the alarm panel reliably. A wireless system can be moved to a new home easily, an advantage for those who rent or who move frequently. The more important wireless connection for security is the one between the control panel and the monitoring station. Wireless monitoring of the alarm system protects against a burglar cutting a cable or from failures of an internet provider. This full wireless setup is commonly referred to as 100% wireless.

Hybrid systems use both wired and wireless sensors to achieve the benefits of both. Transmitters can also be connected through the premises' electrical circuits to transmit coded signals to the control unit (line carrier). The control unit usually has a separate channel or zone for burglar and fire sensors, and better systems have a separate zone for every different sensor, as well as internal trouble indicators (mains power loss, low battery, broken wire, etc.).

Alarm connection and monitoring[edit]


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 first responder (e.g. police/fire/medical) via a direct phone wire, a cellular network, a radio network (i.e. GPRS/GSM), or an IP path. In the case of a dual signalling system two of these options are utilized simultaneously. The alarm monitoring includes not only the sensors, but also the communication transmitter itself. While direct phone circuits are still available in some areas from phone companies, because of their high cost and the advent of dual signalling with its comparatively lower cost they are becoming uncommon. Direct connections are now most usually seen only in federal, state, and local government buildings, or on a school campus that has a dedicated security, police, fire, or emergency medical department (in the UK communication is only possible to an alarm receiving centre – communication directly to the emergency services is not permitted).




Broadband alarm monitoring[edit]





Radio alarm dual signalling[edit]





Listen-in alarm monitoring[edit]


Alarm monitoring services[edit]


Alarm response[edit]





Access control and bypass codes[edit]




False and absent alarms[edit]




False alarm reduction[edit]






Audio and video verification[edit]








Enhanced call verification[edit]

Enhanced call verification (ECV) helps reduce false dispatches 25–50% while still protecting citizens, and is mandated in several US jurisdictions, although the alarm industry has successfully opposed it in others.[8] ECV requires central station personnel to attempt to verify the alarm activation by making a minimum of two phone calls to two different responsible party telephone numbers before dispatching law enforcement to the scene.

The first alarm-verification call goes to the location the alarm originated. If contact with a person is not made, a second call is placed to a different number. The secondary number, best practices dictate, should be to a telephone that is answered even after hours, preferably a cellular phone of a decision maker authorized to request or bypass emergency response.


Independent certification[edit]


See also[edit]


  1. ^ Lee & Wilson 2013.
  2. ^ "NASA Langley Researchers Nab Invention of the Year for Infrasound Detection System". 2014-07-25.
  3. ^ Chilo & Lindblad 2008.
  4. ^ "Perimeter Intrusion Alarm Systems" (PDF). U.S. Nuclear Regulatory Commission. 1997. Retrieved 14 December 2020.
  5. ^ Trivedi, Bijal (14 May 2007). "Hunting Poachers Remotely". MIT Technology Review. Retrieved 26 October 2020. (subscription required)
  6. ^ Chen & Young 1984.
  7. ^ "Bowmark Capital backs £32 million MBO of CSL DualCom". IFSEC Global. Informa Markets. 12 January 2012. Retrieved 14 December 2020.
  8. ^ a b c d e f g Sampson, Rana (2011), False Burglar Alarms 2nd Edition (PDF), US Department of Justice / Office of Community Oriented Policing Services, ISBN 978-1-932582-04-8, archived from the original (PDF) on 2014-08-14
  9. ^ Harrelson, Chuck (2013-09-30), Audio Verification Equals More Apprehensions, EH Publishing, retrieved May 17, 2014


Further reading[edit]

External links[edit]