How Does a Burglar Alarm System Work?

If you have lots of valuables, an insuranceindicators showing which parts of the system
company may insist that you fit a burglar alarmhave been triggered. There is usually a test facility
as well as taking other security precautions. Thisso that you can make sure the system is
rules out d-i-y alarms, since they will almostworking properly and, like the external warning
certainly insist on an alarm installed to BS 4737devices, the boxes are fitted with tamper
which includes a provision for the installingprotection so that the alarm will sound if anyone
company to inspect regularly. Companies who aretries to take the front off the box.
registered with the National Supervisory CouncilWiring up a do-it-yourself system is fairly
for Intruder Alarms (NSCIA) guarantee to installstraightforward: the most difficult parts of the job
to this standard.are concealing the wires and fit¬ting
Before installing a burglar alarm, you should thinkflush-mounted magnetic contacts. Wiring up
about the advantages and disadvantages ofcontacts and the control box can be fiddly; to
having one.wire the warning device you will probably need to
On the plus side is the fact that you have awork up a ladder. The better systems use
visible deterrent to would-be burglars, and thefour-core and six-core wire for detection devices,
alarm going off may stop a burglar getting in orwhich means that the alarm will sound if any wire
cut down the time he stays around if he doesis cut.
get in. There may also be advantages inThe alarm itself is wired in low-voltage cable, but
protecting a window with a burglar alarm ratherthe control panel usually needs a connection to
than a lock so that you can get out quickly inmains electricity via a fused connection unit. If you
case of fire. And for people living on their own -are in any doubt about this part of the job, call in
or elderly or disabled people - there is thean electrician.
additional advantage of being able to attractWire-less systems
attention with many alarm systems. A panicA wire-less system has components similar to a
button could raise the alarm if someone were toconventional wired-in do-it-yourself burglar alarm
attempt to push their way in through the frontsystem, but the communication between the
door.various parts is by radio waves rather than by
On the minus side is the inconvenience ofelectricity. This means that no wiring is needed
activating and deactivating the alarm, and the cost(except between detection devices and their
and problems with false alarms. And if you livetransmitters) and that the control panel can be
miles from anywhere there may be no one tosituated anywhere in the house and moved
hear an audible alarm.around if you want. The control panel itself is set
Burglar alarms which you can install yourself breakby key and tells you if any parts of the system
down into four groups: wired-in systems, wire-lessare not secured before setting the alarm and will
systems, door alarms and movement detectors.indicate whereabouts a break-in has occurred. The
You can also get different types of securitysystem can be divided into zones and
lighting.incorporates a portable emergency transmitter;
Wired-in systemsinfra-red transmitters to detect movement can
This is probably the most common type of d-i-ybe used as well as magnetic contacts and
alarm system. A 'kit' consists of three main parts:pressure pads. The system is very easy to add
a series of detection devices, a warning deviceto and can incorporate a remote dial¬ling
(siren or bell) and a control panel.facility, but this is very expensive.
Detection devicesDoor alarms
The detection devices for this type of system willRather than having a centrally controlled alarm
usually be there to react if someone opens asystem you can instead fit individual
window or door connected into the system.battery-operated alarms to the doors and
Magnetic contacts will cause the alarm to sound ifwindows which are at risk. This makes the
the circuit is broken: the neatest and mostsystem a lot easier to install.
effective are flush-lilting (like mortice locks);Most door alarms depend on movement of the
surface-mounted contacts are easier to install anddoor: the alarm is set either with a key or by
may be the only option on double doors orlapping in your personal code on a key pad. A
metal-framed windows. Pressure pads are fitteddoor alarm can be set to 'instant' (when you are
under carpels (in front of the hi-fi or under one ofin) or 'delay' to allow you time to get in and out.
the steps of the stairs) and will cause the alarmSome door alarms have an additional 'visitor'
to sound when trod¬den on. Most d-i-y alarmsetting which gives a chime or bleep when the
systems have a manually operated panic buttondoor is opened.
(or personal attack button) which is fitted by theMovement detectors
bed or by the front door and will set oil' the alarmDevices that detect unwanted movement in a
(even when the system is deactivated) if youroom work in one of two ways. Either they are
push the button (it can be reset only with a key).infra-red - they detect the body heat of an
Few do-it-yourself wired systems containintruder - or they rely on the breaking of an
movement detectors, but they can usually beultrasonic beam. Either way, the devices are
added as an extra.unobtrusive and easy to install, needing only a 13A
Warning deviceselectrical supply.
The warning device is usually an ear-piercing bellMany movement detectors are disguised as
or siren in a box fixed to a high part of the wallhousehold objects such as hi-fi loudspeakers, but
of the house. They are designed to sound for nononetheless will let off a piercing noise if anyone
longer than 20 minutes (to comply with the law);enters the room they are protecting.
some systems incorporate a flashing light as wellSome movement detectors can be wired to
which will go on for longer. The warning deviceexternal alarms, and some can be included in
usually has its own battery which will cause thewhole-house burglar alarm systems.
device to operate in the event of mains failure orSecurity lighting
the wires being cut. You can usually buy 'dummy'There are essentially two types of security
bell boxes as extras to put on other sides of thelighting you can fit to your house.
house. Most systems can be fitted with anThe first utilises a security light switch which you
internal alarm which goes oil' just before the mainfit in place of an ordinary lightswitch (after turning
alarm sounds.off the electricity). This type of switch will turn
Professionally installed systems may also havethe controlled light on and off according to the
remote dialing where a phone call is made usuallyprogramme set on the switch. A side light could
to a central monitoring station when someonealso be turned on and off by a simple light switch
breaks in, before the audible alarm sounds. Thisplugged into the socket outlet which feeds the
facility is expensive.light.
Control panelThe second type of security light is mounted
This is the heart of the system and is usuallyoutside and is operated by an infra-red sensor,
key-operated to switch the system on and oil'.either incorporated within the light itself or
Most systems have a delay built in so that youmounted separately. External lights, especially
have time to get through the front door withoutpowerful ones, are good burglar deter¬rents,
selling off the alarm; some have different zonesand one that comes on automatically will tend to
so that you can protect different parts of thefrighten them away. This type of light is easy to
house. You might, for example, want to leavewire, requiring only a connection from a fused
only downstairs protected during the night.connection unit inside the house with perhaps
Control boxes are generally mains-powered with afurther wiring if a single detector turns on more
(rechargeable) battery back-up, and many havethan one light.