Burglar Alarm Sensors
The components of a burglar alarm system typically consist of a control panel with
keypad, siren or sounder and a number of different types of alarm sensors that are
connected to the control panel.
There are various burglar alarm sensors which each have different functionality.
Essentially an alarm sensor is a monitoring device and some monitor sound whilst
others monitor movement. Sensors have a trigger threshold, and when the threshold
is exceeded, a signal is sent to the control panel for processing.
For example, the simple, most common alarm sensor is the door or window alarm sensor.
This is often a magnetic read switch and is installed in such a way so that when
a door or window opens, the trigger threshold is reached and the signal is sent
to the control panel. The read switch is attached to the door frame and a magnet
is attached to the door (both encapsulated in plastic holders). When the door is
closed the read switch contact is “made” because of the close presence of the magnet,
thus making an electrical circuit. The control panel is monitoring this circuit.
So when the door opens, the magnet moves away from the read switch making it open,
thus breaking the circuit. This will cause the control panel to take action. This
action could be to sound the alarm immediately, or delay the alarm sounding. The
sensor may the designated as a delay sensor to allow time for the occupants to open
their door and reset the alarm system.
Another common alarm sensor is the Passive Infrared (PIR) motion sensor. A PIR sensor
uses heat to trigger its threshold. It is installed to monitor a room or hallway/walkway
and will trigger when a person walks into the region of the monitoring vicinity
of the PIR sensor. PIR sensors are designed to detect changes in heat – changes
in heat over a few seconds. They do not get triggered through changes in natural
sunlight over a few minutes as not to trigger false alarms.
There are also different types of sensors for safety monitoring. Carbon monoxide
sensors can often be installed and connected to the alarm system control panel.
These sensors monitor carbon monoxide levels in your home and trigger when high
level are detected. These devices are useful for monitoring gas appliances such
as fires, boilers and cookers. Finally smoke alarms can monitor the presence of
the outbreak of a fire in your home. Both these devices could well save you and
your families lives so it’s worth considering installing these devices.
The installation of these devices will involve some sort of connection back to the
control panel. There is a choice of hardwired or wireless sensors. It is worth being
aware of the pros and cons for each before you design, plan and purchase your home
security alarm system.
Wireless alarm systems
are easy to install and cost effective and the average DIY’er can install a system
without having to call a professional installer. However, the sensors will need
batteries which will need to be changed regularly. They also provide the benefit
that if you move house, you could de-install the system and take it with you. This
is attractive for rented properties. A hardwired installation will usually require
a professional installation company but is a more permanent and often more reliable
in operation. There will be no batteries to change and it will probably last longer.
However, installation costs will be higher.