Burglar Alarms

Burglar alarms are now a standard part of the equipment for businesses, and are installed by electricians in shops, offices, industrial estates as well as homes.

Security alarm systems range from simple self-install kits to top of the range networks that require professional installation, but they all stem from the same basic design.

Every burglar alarm comprises three main components:

• A Control Panel (CP)
• One or more Detectors
• One or more methods of signalling that an alarm has occurred

The simplest design has a basic electric circuit built into an entry way. To turn the electricity on or off, part of the circuit is either opened or closed.

When opening or closing a light circuit, you hit the switch. In an alarm, the switch is present to detect intrusion by a door or window opening. Burglar alarms fall into two categories:

• Closed-circuit system - the electric circuit is closed when the door is shut. So long as the door is closed, electricity can flow from one end of the circuit to the other. If somebody opens the door the circuit is opened, and electricity can't flow, thus trigging an alarm.

• Open-circuit system - opening the door closes the circuit, so electricity begins to flow. The alarm is triggered when the circuit is completed.

Close circuit alarms are usually more preferable as a burglar can simply cut the connected wires of an open circuit.

Basic alarm systems with a magnetic sensor comprise:

• a battery powering a circuit
• a spring-driven metal switch built into a door frame
• a magnet embedded in the door, lined up with the switch
• a separately-powered buzzer with a relay-driven switch.

On all modern designs in burglar alarms there is the main unit of the control box. The control box has its own power supply, whilst being linked to one or more alarm circuits. If an alarm is triggered, it can't be cut off until a code is entered into the control box.

With this system, you can make anything a burglar might break into a part of the circuit. For example, you can run thin foil wire across a glass window, so that the broken window will trigger the alarm.

Modern alarms can now either be hard wired or wireless. With a wireless alarm, the equipment operates on a radio frequency passed between transmitter and receiver. The transmitters are in the circuit detectors, while the receiver is either in or attached to the control box.