What is an intruder alarm system ?

What is an Intruder Alarm System?

An Intruder Alarm System is made up of four main sections. These are explained below

Control Panels, or where do all the wires go?

 What are the control panel and the RKP?

 This is the ‘heart’ of the Intruder Alarm System itself. All the decisions are made here. All the parts of the Intruder Alarm are linked to this box; this is why it is usually hidden away! The control panel is connected to the mains electricity and has a battery fitted inside to run the system in the event of a power cut.

A Remote Keypad (RKP) controls the Intruder Alarm System. This is fitted somewhere near the exit point, it is mainly used to switch the system on and off but is also where information is entered or extracted.

 2.     Detection Devices, or how is an intruder detected?

 What is a door contact?

A contact (in its simplest form) is a metal switch, fitted to the doorframe that is kept closed by a magnet fitted to the door. In most cases these are fitted flush into the frame and door but some are fitted surface. Heavy Duty contacts can be fitted to large doors (e.g. garages) and special contacts are available for Roller Shutters.

 What is a P.I.R?

 A P.I.R or Passive Infrared is a device that detects infrared movement (heat). It is the most common form of movement detection fitted to an Intruder Alarm System.

Because the detectors are ‘passive’ they detect rather than emit infrared energy. P.I.R detectors can cover ranges of 60 meters.

 What is a Quad P.I.R?

 A Quad P.I.R is very much like the standard P.I.R but uses two circuits instead of one (each circuit is Dual Element, hence Quad). These types of detectors are far more resistant to causes of false alarms e.g. draughts, small animals and insects etc. These detectors look similar to a P.I.R.

 I have got pets; will they set off the alarm?

Cats and dogs have always made it difficult to design effective and economical Alarm Systems. Fortunately there are now ‘Pet Immune’ P.I.R detectors which can provide similar protection as a standard P.I.R but will ignore cats and small dogs. These detectors do need to be sited carefully.

 What is a ‘Dualtec’ or Microwave Detector?

 A ‘Dualtec’ is a detector that has two detection devices. The most common type is a Microwave/P.I.R but can be any combination of detection devices (Ultrasonic and Seismic being the other most popular). A Microwave detector works by sensing the physical movement of an object (person). These units would be installed in an area that may be prone to temperature fluctuations as the P.I.R and the Microwave circuits need to be activated simultaneously to cause an alarm.

 What is a Personal Attack Button?

 A Personal Attack Button, often called a ‘panic’ button is a small unit that has one or two recessed red buttons. When pressed it causes the alarm to activate immediately. If the system is monitored a signal is sent to the receiving centre and passed to the police.

What is a shock sensor?

 This is a small device usually fitted to a window or doorframe, properly known as a seismic detector. This detects vibrations caused when a door or window is attacked.

 Are there other types of detectors?

 Yes. There are many other types of detection devices that can be connected to alarms. Glass Break detection, Smoke detection, Ultrasonic Infrared beams and Lace Wiring are just a few. A detection device can be found to suit any situation.

 3.     Sounders, or how do I know the alarm has gone off?

 The Bell Box

 Every Intruder Alarm System will have an outside sounder usually fitted at high level and which makes a lot of noise. It has anti-tamper protection and a separate battery fitted, it also has a Strobe light that flashes when the sounder activates. The outside sounder will ring when the Intruder Alarm has been activated and must switch off after fifteen minutes, but will reactivate if any sensor within the property is activated.

 The Internal Sounder

 The internal sounder is fitted somewhere inside the protected area. This will indicate fault conditions as well as full alarm activations. There may also need to be more than one internal sounder fitted in larger buildings.

 The Communicator

 The communicator will dial out to mobile phone, landlines or an alarm monitoring centre if the alarm is activated. Owners or key holders will be made aware of the type of event by either voice message or text message. If the owner / key holders telephone is not answered the communicator will dial the next programmed telephone number. Monitoring centres will despatch the emergency services / police.

Depending on the model and type of system, the communicator is either built into the main alarm panel or is a separate unit which is wired to the main alarm panel. The communicator is usually connected to the telephone line in the property or can be a GSM unit which uses a SIM card identical to that which is installed in a Mobile phone, the GSM would be used if a wired telephone line is not available at the premises. The only ongoing cost of using a communicator is the price of the telephone call or text message if the alarm is activated. A monthly charge is usually applicable if connected to an alarm monitoring centre.


Alarm systems may differ in other countries due to varying regulations but the principle is always the same. For information regarding some types of burglar alarm systems in this case, Northern Ireland, see www.homesecurealarms.co.uk



I have worked in the electronic security industry for over 20 years. I have my own business supplying and installing alarm systems.


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