DIY Burglar Alarm Systems

In the past burglar alarm systems were usually fitted by professional alarm companies; however there are now burglar alarm kits and devices which are suitable for DIY installation. In most cases these are easy to install and offer a considerable saving in cost, especially since there is no need for the yearly maintenance contract normally stipulated by professional installers.

Warning If your premises contain items of high value, a DIY installation is unlikely to be accepted by leading insurance companies who will insist on an installation which meets British Standard 4737; always check this point with your insurance company before you decide on any alarm system.

When considering an alarm you should bear in mind the implications of living with such a device and the snags involved. For example, all the doors in the house must be secured every time you go out, even if only for a short while. When an alarm is installed, it is most important to notify the police and give them the name, address and telephone number of at least one person who holds keys of the house and of the alarm; otherwise neighbours will be considerably disturbed if an alarm is activated and rings for hours at night or over a weekend.

Wired circuit

Most conventional alarm systems include devices which operate both open and closed latching circuits. The term latching means than when the device is activated, the alarm can only be switched off at the control panel.

Closed circuit

Closed circuit devices most often used are magnetic switches, sometimes referred to as surface contacts; these are supplied in pairs. One part, which fits to the moving part of a door or window, contains a magnet; the other, which fits to the door or window frame, contains a reed switch. When the switch is correctly fitted and the door or window is closed, the proximity of the magnetic field (from the magnetic contact) causes the reed switch to close. When the alarm system is on, opening a door or window will result in the alarm sounding since the reed switch is opened by the removal of the magnetic contact and its field.

Magnetic switches have the advantage that a good degree of tolerance — normally up to 19mm (Sin) — exists; therefore the normal slight movement or vibration of a door or window caused by wind is unlikely to activate the alarm, since the reed switch will be held by its magnetic partner.

It is important the catches on all contacted doors are checked for efficient operation, since a door can click open hours after being closed if the tongue does not engage properly in the staple; this would, of course, set off the alarm.

Open circuit

The most common open circuit device is the pressure mat. As its name implies, this is a device in mat form which activates the alarm when someone stands on it. Basically it comprises two layers of tin foil separated by a foam rubber pad and connected by two cables to the alarm system’s control panel. Weight or pressure on the mat overcomes the insulation of the foam pad, contact is made and the alarm will sound.

Before installing pressure mats in rooms or on stairs, bear in mind pets must be restricted in these areas; even a cat can set off the alarm by jumping from furniture onto a pressure mat.

Planning the system

A good wired circuit alarm system should inhibit initial intrusion, raise the alarm if intrusion occurs and ideally scare off vandals and burglars before damage is done or valuables are stolen.

The system should comprise:

A strong metal outside bell box containing a loud 150mm (6in) bell; the box should be protected with an anti-tamper device.

An inside bell to ensure the alarm sounds if the outside bell is tampered with. This is an essential item since, if an intruder is determined, he could remove the outside bell box and silence the bell. Also an outside bell may not be heard inside the house if a television is switched on for example.

A control panel which allows easy installation.

At least seven alarm activating devices.

A panic button facility for operating the alarm independently.

Apart from the basic equipment, there are other devices whiCh may be added to the system.

Shunt switches Where an alarm system does not include an entry/exit timer, a shunt switch should be fitted to the exit door. This key-operated switch bypasses the magnetic switch on the door and allows you to leave and re-enter the premises without sounding the alarm; it must be unlocked as you go out through the door and locked again behind you. The disadvantage of a shunt switch is that an intruder may be able to obtain a skeleton key and enter without sounding the alarm.

As an alternative you can install a good quality mortise lock fitted with a microswitch which is wired into the alarm system; this brings the exit door into the system when the door is locked and takes it out of the system when the door is unlocked. There is no danger of false alarms since you cannot enter the house without unlocking the mortise lock. Window foil Some DIY alarm manufacturers recommend fitting foil to fixed windows in a closed series circuit. The foil is 6mm (*in) wide and has an adhesive backing so it can be stuck to the window surface; terminal blocks on the foil allow it to be wired to the alarm system’s control panel. If the foil is broken, the alarm will sound.

Trembler switches These switches, which measure approximately 65 x 38mm (21 x liin), adhere to the window. If the pane is broken, the trembler contacts touch or break and activate the alarm. Check whether your switch is open or closed circuit.

Installing the system

Wired circuit alarm systems are designed to create a protected area which ensures any intruder who attempts to enter the main part of the house will activate the alarm. Before you begin work on the installation, make a plan of the house and indicate the position of the equipment and the protected area; this will give you a clear picture from which to work. When deciding on the layout for the wiring, always take the most direct route to keep down the amount of cable needed.

A good alarm system will include comprehensive fitting instructions and you should always follow these carefully. There are some general points, however, which you should bear in mind.

Ideally the outside bell should be as near to the control panel as possible and should be fixed at first floor level to the side of the house so it is visible from both front and rear. You will need a long masonry drill bit to make holes right through the outside wall to take the bell cable.

The control panel should be fixed in a concealed position inside the protected area.

Wiring should be neat and concealed wherever possible. Secure it with staples at 1 m (or 3ft) intervals and make all electrical connections carefully to avoid false alarms.

Pressure mats should be placed underneath the floor covering next to the floor; they are not suitable for fitting under small rugs or loose-laid carpet, since the connecting wires would show and the mats would be subject to movement and unnecessary wear. Fix the mats into position with double-sided adhesive tape and secure them with tacks if suitable lugs are provided. Make sure there are no particles of grit or other sharp objects trapped beneath the mats.

The panic button can be fixed by the bedside and/or close to the front door. If it is beside the door, you should also fit and use a door chain ; in the event of an attempt to force entry, the chain will hold the door for sufficient time to allow you to press the panic button.

Ultrasonic units

Most house alarms do not cover all the windows; this permits an intruder to enter one room and not be detected until he opens an interior door or steps on a pressure mat. While this is acceptable if the intruder breaks in through the kitchen or bathroom for example, it is not good enough if the first room entered contains valuable items. To overcome this problem, space detection devices have been developed. These are normally devices which work on the principle of ultrasonics, transmitting and monitoring inaudible high frequency sound waves; any change in the returning frequency — as would be caused by the movement of an intruder — will activate the system.

A self-contained ultrasonic unit usually resembles a hi-fl speaker, which enables it to blend unobtrusively into any room. The unit is plugged directly into the mains and includes a built-in siren or electronic sounder, stand-by batteries in case of mains failure and entry/exit timers which allow the person switching on the system to leave the protected area before the alarm sounds. Other features include an alarm cut-off and reset; if the intruder leaves, it will automatically reset to guard against repeated entry. A walk-test facility enables you to set the ultrasonic pattern and a false alarm correcting circuit monitors movement such as heat convection and flapping curtains and prevents them activating the alarm.

This type of system is easy to install and offers excellent protection, since ultrasonic devices have become much more reliable and the original tendency to sound a false alarm has been greatly reduced. However, the individual units are quite expensive and, since one unit is usually required for each room, cost could be prohibitive. The units are however, particularly effective in terms of cost in an open plan situation when a single unit can protect a large area.

Combined systems

The best protection can be obtained by incorporating a fixed ultrasonic unit into a conventional alarm system. A typical combined system includes ultrasonic master and slave units to monitor two rooms, a closed circuit using magnetic switches to protect doors and windows and an interior and/or electronic sounder.

Ways and this can be controlled if the outside doors are insulated properly. Fit draught excluders or provide a heavy curtain which can be pulled right across the entrance. A really chilly hallway can be improved by fixing a small wall-mounted gas or electric heater or a central heating radiator. Alternatively an effective method of insulating a hall is to build a porch and install double doors.

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