How Burglar Alarms Work

Though they protect out home, belongings, and evenburglar alarms work.
our lives from outside dangers, many of us don'tHow Burglar Alarms Work: Basic Motion Detectors
understand how burglar alarms work.Circuit alarms are highly effective around the outside
In the Good Old Days, how burglar alarms work wasof your home and business because criminals have to
simple -- the dog barked. But now, how burglarget past the perimeter to get inside. But once they
alarms work has become a multi-million dollar scienceare inside, their movements are too unpredictable to
in an industry that is growing rapidly and advancinghave circuits everywhere inside the house. So then
every day.you have to rely on motion detectors.
We asked Home Security Store's founder and ownerYou run into motion detectors all the time when you
Stacey Mcbride to help us explain how burglar alarmsare approaching an automatically opening door that
work.uses a radar-based motion detector. A control box
"You'll find that there's a huge variety in alarmabove the door sends out radar waves (either
systems, from do-it-yourself kits to whole-housemicrowave or ultrasonic) and then waits for those
wired systems. But most alarms work on the samewaves to be reflected back in an irregular pattern,
basic principles, and even the most complex systemindicating a presence is in the space. For automatic
is based on a pretty basic concept of how burglardoors, that reflection detection opens the doors,
alarms work," says Stacey.while in an alarm system, it triggers the alarm.
How Burglar Alarms Work: Circuit AlarmsSo a motion detector works by constantly monitoring
The most common first line of defense when ita room for irregular wave patterns. When a room is
comes to how burglar alarms work is to use theempty, the radar waves behave one way. But when
circuit principle. You can have two kinds of circuitmotion is presented in the room, the pattern changes
alarm: closed circuit or open circuit.and the sensor detects the change to trigger the
The basic concept is the same: you run an electricalalarm.
circuit through a door or window. In an open circuit,How Burglar Alarms Work: More Advanced Motion
the electrical current is not completed until the doorSensors
or window is open, which then triggers the alarm.Other than radar-based motion detectors, there are
The only drawback to this system is that all thealso photo-sensor motion detectors. How burglar
criminal has to do is cut the wires to prevent thealarms work in this case involves beams of light. You
circuit from being completed. In a closed circuit, theaim the beam of light at a light sensor across a
current is broken when the door or window is open,passageway in your house. When someone walks
triggering the alarm. The all-important control boxthrough it, the light beam is broken and the sensor
monitors all the doors and windows and once thetriggers the alarm.
circuit is broken, the control box will keep soundingMore advanced are passive infrared (PIR) motion
the alarm till someone resets it with a predeterminedsensors. These motion detectors see the heat given
code.off by a body. Though the infrared energy tends to
The control box is often placed in an out of the wayfluctuate in any given space, a PIR motion sensor
place so a criminal can't easily find it and break it.only triggers the alarm when the energy rises rapidly,
The closed-circuit method of how burglar alarmsi.e. when a human, whose average body temperature
work can be used all around the perimeter of theis 98.6 degrees, enters an otherwise approximately
home. Just create a circuit that will be broken when a80-degree room.
criminal tries to enter and you have an alarm system.If you have a motion sensor alarm system, there is
To make sure the alarm goes off if the window isusually delay of a few seconds on the control box to
broken rather than simply slid open; make the glassgive you a chance to disengage the alarm when you
itself a circuit by running a current through it with aenter the room.
thin foil wire.How burglar alarms work has advanced beyond
Even floor mats can be made into an open circuitbarking dogs and strung-up pots and pans. The
alarm. When someone steps on the mat, the circuit isscience of how burglar alarms work applies
completed and an alarm sounds.measurements of time and space, incorporating the
You can surround your home with a closed circuitwhole room into its security. A good alarm system
alarm system that will sound the alarm when anwould combine both circuit and motion sensor alarms,
intruder breaks the circuit. But once the criminal isgiving you two lines of defense when it comes to
inside, you need a whole different approach to howhow burglar alarms work.