These days the intruder sensors mostly used are what are known as Passive Infra Red sensors. When installed correctly they are normally extremely stable and nuisance alarm free. The sensor operates by detecting changes in the levels of a narrow band of infrared energy in its area of view. All objects in an area transmit infrared energy. When a person moves into the area, the body heat of the person changes the levels of infrared; this change is what the sensor detects.
Infra red sensors are installed in areas where possessions of financial or sentimental value are kept. This could be in the dining room, lounge room, family room and master bedroom. A sensor can cover an area of up to 15 meters x 15 meters. At additional cost, pet tolerant sensors are also available. These units will ignore a pet (up to 38KG and 0.75 meters high) in the area, but still detect a walking intruder.
The system should include at least 1 or 2 smoke detectors that are installed to the living and bedroom areas of the home. Door switches and glass break sensors can also be installed to protect the perimeter of the premises. These devices are normally used in conjunction with internal passive infrared sensors. The major advantage of perimeter protection is that the entire perimeter alarm can be activated whilst you are in the house. The major disadvantage is that the cost of installing this type of system could be around $2,000 to $3,500.
Around 85% of systems are hardwired, where the sensors, keypads, etc are connected to the control panel by cables. An alternative method is to use wireless devices that communicate with the control panel using wireless technology. Utilising wireless systems has advantages when used in locations that would be difficult to hard wire and also in rental properties, as the cost of re-installation to a new site is minimal. The disadvantage of using wireless systems is that the installation technician must have a clear understanding of installation techniques, as well as the do’s and don’ts of wireless system technology.
The alarm control is the brains of the system and continuously monitors the state of the system. It contains the microprocessor electronics, power supply and re-chargeable, standby batteries. It is normally connected to a keypad that enables authorized persons to arm and disarm the system. Today’s modern systems are easier to operate than a microwave oven. They normally have 3 operating modes; away armed, at home armed and disarmed.
The system will typically provide single touch buttons to arm the system, and a 4 digit code is entered into the keypad to disarm the system. In the home arm mode of operation all of the areas that the occupant will be moving in are automatically isolated from the system, enabling a level of protection while they are in the home. A number of indicator lights on the keypad show the system’s operating mode, as well as system information. The control panel is normally installed in a discrete location such as a wardrobe and the keypad is mounted in a convenient location such as near the entrance door. At an additional cost, convenient remote control “key ring” style wireless transmitters can be used to arm and disarm the system.
There are 3 methods of generating a warning that the alarm system has activated; a local sounding system that triggers internal and external sirens, a monitored system that will transmit a signal down the normal telephone line to a central monitoring station and a self monitored system that will transmit a signal down the telephone line to a telephone, pager, or mobile telephone. Systems using remote monitoring may also have local warning sirens. External sirens, are mounted in weather and tamper resistant enclosures that contain tamper switches that will activate the system if the siren cover is removed. A blue flashing strobe that latches on in the event of an alarm, and remaining on until the system is disarmed is normally incorporated into the external siren unit.
When a monitored alarm is activated, the control panel will dial the pre-programmed telephone number of the central monitoring station.
As soon as a communication link is established, the control panel will transmit digital information to the central station receiver describing
the premises location and the area that has triggered the alarm. Information is then displayed on a computer terminal showing the name and address of the premises, a description of the zone in alarm, relevant emergency telephone numbers and the actions require to respond to the event. The response could be to call a relative, call the fire brigade or send an armed guard etc.
A chime function can also be provided. This function is enabled in the disarmed operating mode and will momentarily “beep” the keypad or a buzzer if a particular zone(s) on the system is opened. The zone could be the front and back doors, swimming pool gate, gate to the street, etc and provides an additional level of security to the system.
Alarm system requirements are described in the Standards Australia document AS2201.
For more alarm system details, please download this PDF.