How To Fit A Burglar Alarm

One of the best things you can learn in DIY and home security is how to fit a burglar alarm. It is always a wise investment — not only to safeguard your valuables but also to give protection against vandals. There’s a range of DIY systems on the market all designed with ease of fitting in mind.

Your first line of defence against intrusion into your home should be strong door locks and lockable window fastenings. But a good burglar alarm is the best deterrent. With modern electronics they have become increasingly sophisticated and harder for burglars to defeat; which has meant a consequent increase in the security of your home.

How To Fit A Burglar Alarm

Burglar alarm systems

Most systems consist of the following:

A control unit. This incorporates the on/off switch and sets off the alarm when one of the sensors detects an intruder. Many incorporate an automatic delay so that you can activate the system, then leave the house through a door on which a sensor is mounted without setting off the alarm.

An alarm unit. This usually consists of a bell or siren mounted in a box and fitted on a prominent part of an outside wall as a visual deterrent. The alarm (like the control unit) is battery operated so that power cuts don’t deactivate it, and is fitted with an antitamper device so that any attempt to move or destroy it sets off the alarm.

Sensor units. There are usually two types —magnetic sensors fitted to doors and windows, and pressure pads which are laid under carpets on the likely path of an intruder as he moves through the house. A third, but less common, type of sensor is the infrared movement sensor. This works a little like radar, detecting movement in a darkened room to set off the alarm. It is less common in DIY installations, but frequently found in pro fessional systems protecting commercial premises.

Wiring. Most wiring consists of two core flex running between the various components of the system, but it is possible — even on DIY installations — to get antitamper wiring which sets off the alarm when cut or bridged.

For obvious reasons, many technical details are revealed only in the manufacturer’s instructions. Your choice of alarm system depends very much on your requirements, and you are advised to shop around, consulting manufacturers before deciding which system is best. However, except in the most unusual circumstances, there is little to choose between many of the DIY systems.

Preparation and planning

Whatever system you decide on, you must read the instructions carefully and familiarize yourself completely with all the component parts.

Draw a plan of your home to decide where the alarm’s sensors — magnetic or pressure pad devices — should be located. Choose where the control unit is to go — in general it should be sited as close to your front door as possible so that you can prime or switch off the system on leaving or entering the house without the alarm going off (though not all systems work in this way). Locate the siren where it can be seen and heard. If you fit it to an outside wall where the sound will be muffled by a tall hedge or outbuilding, you’ll lose not only the sound of the siren but also the visual deterrent that sirens provide.

Where valuables are kept in a particular room fit a combination of alarm sensors and stout locks. Remember also that a burglar will generally enter a house by the easiest and least observable route so that is where adequate alarm protection is most needed.

Tools for the job

You will need a power or hand drill, a 19mm flat drill bit for recessed contacts, a 4mm wood twist drill, No.10 masonry drill bit, screwdrivers, a sharp chisel, tack hammer, pliers, wire strippers, and, in some circumstances, a long masonry drill bit to bring wires through external cavity walls. In addition to any of the tools you don’t have and the kit itself, you will probably also need to buy the appropriate gauge of wiring for interconnec tion, (the instructions will detail this), batteries, cable clips, and pins.

Test the system

Test the major components of the alarm system before attempting installation. This serves a dual purpose — it will enable you to ensure that all the equipment is working correctly and also gives you a chance to familiarize yourself with the components.

Follow the maker’s instructions for the connection of batteries and temporary disconnection of the antitamper device, if neces sary, and then go through each of the specified test procedures as instructed. This way you can be sure that the system will only actuate in `anger’.


A typical layout for an alarm system in a twostorey house. The siren should be mounted high up on an outside wall, and prominently positioned to serve as a deterrent to wouldbe burglars. The wiring from the control unit passes through the wall in to the back of the siren, leaving nothing exposed and vulnerable.

The system’s control unit is concealed under the stairs where it is within easy reach of the front door. The sensor on the front door is part of the entry/exit circuit so that it is possible to enter or leave the house without the alarm sounding when it is switched on. The rest of the sensors are divided between two zones: zone 1 is downstairs, zone 2 is upstairs. They can be switched on and off independently to protect part of the house while the family are in another part. The ‘panic button’ is mounted beside the bed and activates the siren whether the alarm system is switched on or not.

INSTALLING THE CONTROL UNIT AND SIREN The control unit is the heart of the burglar alarm system and controls all its functions.

Site the control unit in a convenient position close to the main exit of your home or wherever the instructions specify. Understair cupboards often provide ideal locations.

Using a masonry bit, drill into the wall at the planned position, plug the holes with wall plugs and screw the back plate to the wall.

Fit the siren on an external wall out of a potential burglar’s reach but as close to the control unit as possible. Often this means high up on a front wall close to the eaves.

Ideally, you should run the cable used for connecting the control unit to the siren up through the interior of the house and feed it through the wall directly into the siren.

Follow the maker’s instructions closely for this part of the installation as the siren unit will probably include a number of fail safe and other antitamper devices.

With both control unit and siren in position, the two units can be connected.

1. Having bench tested the system, fit the control unit, preferably out of sight and close to the main entrance of the house.

2. Fit the siren in a prominent spot high up on the outside wall.

Try to run the wire straight into it through the wall — leave none exposed.

3. Make the connections according to the manufacturer’s instructions and fit any batteries required at this stage.


Route all cabling as inconspicuously as possible. Cable can be hidden behind skirting boards, channelled into walls or run under carpets. Ensure that you make good electrical connections — the alarm will fail otherwise.

Measure the length of cable you need —allow a little extra for errors — to make a neat job. Normally 0.5A twocore cable is required — this is available at most electrical or hardwear stores.

Route the cabling as appropriate between the sensor and the control box. Make sure that enough cable is left to make a connection to the terminals easily.

Use wire strippers to bare the cable. Remove about 5mm of insulation material from each core. TIP: Check each stage of the wiring for continuity — in other words that a circuit has been made. This can generally be carried out at the control panel by operating the zone or selector switch governing the particular circuit. This will simplify any fault finding that might be needed when the installation is complete.

Decide on your major exit/entry route. Normally this will be the front door, but any external door is appropriate. Do not place pressure pads on this route. Normally the time allowed for opening and closing the exit door after the control unit is switched on is about thirty seconds, so make sure you can reach the door and leave in that space of time. Not all alarms use this system, however, so check with the instructions.

Some manufacturers supply 4core cable for their systems which can be fitted in such a way that cutting it sets off the alarm. Most do not specify which colours of core should be used for which connection — to foil thieves —so choose for yourself, but make a note somewhere for reference if problems arise.


Basically these sensors are magnetic switches that will detect if a window or door is opened or closed. The switch assembly consists of two parts — the switch itself, which you fit to the window or door frame, and the magnetic actuator, which goes on the door or opening window. The gap between the two sections should not be greater than 6mm when the door or window is closed.

Hide the sensors from immediate view. An ideal location is at the top of doors and windows.

Using a suitable drill bit or chisel, cut or drill into the centre of the door or window frame edge to a sufficient depth to house the sensor comfortably.

Repeat the process on the fixed frames but add a little more depth to allow for the passage of the cable.

If a flush fit is needed, you will have to chisel away sufficient framework to allow for the sensor flange.

For hidden cables you will need to drill through the outer or upper edge of the fixed frames into the hole previously cut to locate the sensor.

Surface sensors can also be obtained. These are ideal for use where drilling into the door or window frames is not possible — if you have metal frames for example. Consult the manufacturer before you buy.


A pressure pad is sensitive to weight and will actuate even through the thickness of a carpet when someone is standing on it.

Beware though, that the weight of a dog — or even a cat — could cause the pad to operate and sound the alarm.

Ideal locations for a pressure pad are at the threshold of a door, on stair treads and beneath windows. If necessary, a pressure pad can be located directly in front of a particularly valuable item such as a wall safe or freestanding security cabinet.

Place pads directly on the floor and not between underlay and carpet. The surface of the floor must be clean and free from grit or abrasions.

Secure the pads using either adhesive tape or tacks pushed through the fixing tabs on the outside of the pad.

Connect the pads to the control box as instructed in the maker’s handbook and test the circuit to ensure that it is operating satisfactorily.

A personal attack button will operate the alarm whether or not the (wtrol unit is switched on. Fitted in a bedworn or close to an exit this ‘panic button’ will help you to summon help if necessary. Be ireful not to locate the button where young Itildren might activate it.


Living with an alarm

Pressure pads can become a nuisance if some form of discipline is not imposed on your I amily: it is all too easy to forget the alarm is switched on, especially during the day. Your first task must be to educate the family —especially younger members — to check the alarm is not switched on when they are moving around. A common mistake is to lay pressure pads under the carpet near an upstairs WC.

Remember also that the police don’t take kindly to false alarms, however much they approve of home owners fitting burglar alarms.

And there is nothing more infuriating to your neighbours than an alarm which comes on while you are away, but cannot be switched off.

If several of your neighbours have alarm systems fitted, it is worth setting up a ‘selfhelp’ group: if one of the alarms goes off, arrange between yourselves for someone to call the police to investigate. Quite apart from the security implications, it improves relations between yourselves. Relations will be improved even more if neighbours leave front door keys and alarm keys with trusted friends nearby so that an alarm which goes off accidentally can be switched off.

Prevention, as the police will always tell you, is better than cure. In fitting a burglar alarm system and using it properly, you are doing yourself a favour while making the police’s job of crime prevention much easier.


Before fully testing the complete alarm system, follow the maker’s instructions for installing any necessary batteries.

You might need assistance to operate pressure pads and magnetic sensors and make sure that all components are properly secured.

Close all doors and windows fitted with sensors and reset personal attack buttons and remove activating keys.

Check, by pressing zone testing buttons, that all the systems are clear.

Now test each pad and sensor by opening doors and windows and applying weight to the pads. If you keep the appropriate zone test button depressed, activation will be indicated by the test light going out.

Repeat the test for all zones by following the maker’s settingup instructions.

A final tip: in case you lose the control keys, leave a spare with a trusted neighbour, or try to get a replacement key cut.

Leave a Comment