| personal attack (PA) zone near to the
front door which will trigger the alarm instantly when pressed. One zone, usually connected to the front or back door, is called the ‘Entry/Exit Zone’. This zone is fitted with (often programmable) time delays which allow you to leave the house having set the alarm, as well as allowing (say) 30 seconds for you to disarm the alarm upon entry detection before firing the sirens. Apart from the magnetic sensors already mentioned, the other main choice for covering a whole room is the passive infra-red (or PIR ) movement detector. This is a motion detector that works by sensing moving body heat in its field of view. A PIR is not triggered by moving curtains or lights being switched on, nor by slowly changing heat sources like a radiator or storage heater, but pets may trigger the sensor. Some PIRs use special lenses that look up away from the floor, but cats with a tendency to run up the curtains may well cause problems! The various sensors fitted to a burglar alarm system are wired to each other and to the control panel using multi-cored cable. Door and window switch sensors generally require a 4-wire connection. One pair of wires are connected to the zone ‘alarm’ terminals. |
| A magnetic switch sensor combined with
a transmitter is used for windows and doors, and some sensor/transmitters allow
you to wire in several additional normal magnetic switches for a large window
with several casements, for instance. PIRs are the easiest sensors to fit as they need no wired connections whatsoever. Simply set the internal switches to indicate which zone the sensor belongs to, connect the battery and fit the unit about two metres up on the desired wall.  All of the sensor power supply and sensor loop wiring on modern burglar alarm systems is low voltage and poses no shock hazard, provided the control panel has been properly fitted. The control panel of mains operated systems will need wiring into a separate fused unswitched spur from your mains supply. Follow the instructions provided with each panel for details of mains wiring and earth connections. Note that working on a system with power applied risks shorting the auxiliary supply and blowing the fuse. If all PIRs stop working, this is the most likely cause. |
| This pair will be shorted by a
magnetic switch when the window or door is closed (a magnet mounted on the
door/window will be in close proximity to the switch), and opening the door
will result in the switch opening the loop. Another pair of anti-tamper wires
are fitted to each sensor, which are shorted under normal conditions by a
switch that is held in place by the screws securing the sensor casing. If the
screws are removed, the ‘tamper’ loop will be broken and the panel
will sound the sirens. PIRs need 6 wires; 2 for power, 2 for alarm and 2 for
tamper and most bell boxes also require a 6-wire connection. Therefore, a good
choice is to use a reel of 6-core cable for the whole installation.
Apart from the magnetic switched sensors and PIRs already described, there are a few special sensors such as glass break detectors, motion or shock sensors, photoelectric beam break sensors and pressure mats.  The zone arrangement on a wireless system is much the same as with a wired one, with several separate zones to cover different areas and 24 hour PA and tamper zones. The obvious difference is that the |
| sensors within a zone do not need
wiring together and usually identify their zone number to the panel by
transmitting a digital code to the receiver. The power supplies in mains operated systems can often be backed up by rechargeable batteries, so that your home will still be protected in the case of a power cut or if the supply cable is tampered with. Likewise, most bell boxes have a rechargeable battery within them, making it very difficult for a burglar to disable the system. Cutting the lead to the bell box (which should, in any case, not be accessible from the outside of the premises) will result in the bell box sounding. Note that most bellboxes normally sound only for a predetermined period (usually up to 30 minutes) as required by legislation. Many alarm control panels have a separate output which remains switched on indefinitely after the alarm is triggered and this is usually connected to a strobe beacon on the bellbox so that you may see upon return to your home that the system has triggered. Take a good look at the system kits and burglar alarm accessories featured in the security section of the Maplin catalogue. If you have any questions, or would like to discuss installation of a security system in your home with our trained staff, please call into one of our stores or call our Technical Helpline for a prompt and courteous service. |