Burglar alarms have become standard equipment in stores and other businesses, and they're becoming increasingly common in private homes as well.
If you've ever shopped for a home security system, then you know there are a wide variety of options available.
These systems range from do-it-yourself kits you can pick up for $10 to sophisticated whole-house security networks that must be installed by professionals. But, as it turns out, most alarm systems are built around the same basic design concepts.
In this article, we'll examine these concepts and explore a few specific alarm designs. As you'll see, some of the most effective alarm systems are also the simplest.
Burglar alarms are networks of integrated electronic devices working together with a central control panel (Brain) to protect against thefts and other possible illegal entries, as well as home intruders.
We can find many names for the burglar alarm, and the most basic definition of a security system is found in its name. Its literal meaning is something secured through a system of interworking components and devices.
It is a fact that you are much less likely to suffer a break-in or burglary if you have a well fitted and maintained burglar alarm.
They provide essential warning of intruders on your premises, earning them their status as staple pieces of security equipment for many homes and businesses.
In this article, we'll be answering commonly asked questions about these pieces of kit, including "what is a burglar alarm?" and "how do burglar alarms work?".
The Importance of Burglar Alarms
The question of why burglar alarms are essential for homes and businesses alike is easy to answer. Simply put, quick action is critical during break-ins, and burglar alarms facilitate a fast response by alerting people in the vicinity to compromised security as soon as it occurs.
It's therefore essential to know the basics of a burglar alarm system and understand what they are, their uses and most importantly, how they work.
They come in a wide variety of configurations, but generally, how alarms work is with a network of motion detectors and door and window sensors integrated with a control panel. These elements all work together as one system to detect breaches in your home or business and alert you or the authorities.
The most basic burglar alarm systems monitor the perimeter of a home or building for breaches, such as opening a door or breaking a window. They do this by creating an electric circuit, called either an open-circuit or closed-circuit.
A closed circuit is the most common. When an electric current is constantly running around the home's perimeter, breaking the course – by opening a door or window – cuts off the electric current. This trips the alarm system and sets off the corresponding alarm. Closed-circuit systems are also tripped if the burglar cuts the power, as the circuit is broken.
In an open-circuit system, electricity only flows when the trigger is activated – opening the window, for example – and completing the circuit sets off the alarm.
Door and Window Sensors
Burglar alarm circuits are triggered in a variety of ways. They can be set off by Door Sensors; these have magnetic switches embedded in the door frame that aligns with a magnet in the door.
When the door is closed, the switch is pulled shut and completes the circuit. When the door is opened, the course is broken, triggering the alarm relay. This same design is commonly used for Window Sensors, too, where a switch is placed in the window frame and a magnet in the door itself.
Another common trigger is a small button embedded in the door or window frame that is pushed in when the door or window is closed but decompressed when they are opened. As the button springs open, it triggers the alarm system.
Uses of Burglar Alarms
So, what are burglar alarms used for – or rather, where are burglar alarms used?
Burglar alarm systems can be used in a diverse range of applications, including:
- Industrial areas such as offices, warehouses and factories
- Residential homes and garages
- Commercial premises including shops, restaurants and hotels
- Storage facilities
Above is a simple summary of the uses, but alarms can benefit any location where security could be improved.
How Burglar Alarms Work
It's important to understand that there are a vast array of burglar alarm systems available on the market, all suited for different applications and types of clients. It is also essential to consider what action you might like if and when the system is triggered.
The three main types of burglar alarms include:
- Bells-only systems, whereby just an alarm is triggered, and that's all
- Systems with speech dialers or communicators that will send a message to several nominated phone numbers
- Monitored systems, where signals from the alarm system are sent to a particular call centre and then acted upon by external means
Whatever the type, most burglar alarms work by a similar series of steps:
- Motion is sensed: When a door or window is shut, the contact of the door or window in the frame is detected by door and window sensors. Motion sensors can also be placed strategically around the premises, which detect motion and trigger the alarm countdown. The perimeter of a site can be protected using a variety of detectors, too.
- Control panel is alerted: All installed components, including sensors, are linked to a control panel and all information from the detectors and sensors is sent here. If this contact is disturbed and the circuit is broken, the alarm countdown is then triggered.
- An alarm is sounded: If an abort code is not entered, the alarm will sound. The system is connected to an external bell or siren, which is usually located on a wall outside the property. It is this device that emits an alarm to alert people to an intrusion. There is also an internal sounder to alert any occupants of the building that there has been a detected event, which also acts to deter the intruder.
- The alarm is deactivated: Users activate and deactivate the alarm system using this control panel, either by using a fob or a numbered code. Smartphones can also now be used to remotely set and unset alarms via apps.
Breaking the Circuit
Other than the family dog, the most basic burglar alarm is a simple electric circuit built into an entryway. In any course, whether it's powering a flashlight or a computer, electricity only flows when you give it a path between two points of opposite charge. To turn the electricity on or off, you open or close part of the circuit.
To open or close a flashlight circuit, you throw a switch. In a burglar alarm, the controller detects the act of intrusion -- opening a door or window, for example.
These sorts of warnings are divided into two categories:
- In a closed-circuit system, the electric circuit is closed when the door is shut. This means that as long as the door is closed, electricity can flow from one end of the course to the other. But if somebody opens the door, the circuit is opened, and electricity can't flow. This triggers an alarm.
- In an open-circuit system, opening the door closes the circuit, so electricity begins to flow. In this system, the alarm is triggered when the course is completed.
There are many ways to build this sort of circuit into an entryway. Closed circuits are usually a better choice than open circuits because an intruder can deactivate the open circuit by simply cutting the connected wires.
A magnetic sensor in a closed circuit consists of a few simple components. For the most basic design, you need:
- 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 busser with a relay-driven control.
When the door is closed, the magnet pulls the metal switch closed, so the circuit is complete.
The current powers the relay's electromagnet, so the busser circuit stays open. When you move the magnet by opening the door, the spring snaps the switch back into the open position. This cuts off the current and closes the relay, sounding the alarm.
You can also build this sort of system into a window. If an intruder pushes a window open, the magnet slides out of line with the switch, and the busser is activated.
Another simple burglar alarm uses a small button as the switch. The button is embedded in the door frame, so closing the door pushes it in. When somebody opens the door, the button is released, changing the circuit and sounding the alarm.
With just a battery and busser, these designs make for somewhat flawed security systems. After all, the burglar only needs to close the door again to turn the busser off. That's why most modern burglar alarms incorporate another piece into the circuit -- the control box.
The control box is hooked up to more alarm circuits, but it also has a power supply. It monitors the circuits and sounds the alarm when closed or opened (depending on the design). But once the alarm is triggered, the control box won't cut it off until somebody enters a security code at a connected keypad. For added security, the control box is usually positioned in an out-of-the-way spot, so the intruder can't find it and attempt to destroy it.
Using this basic concept, you can create all sorts of alarm systems. Just imagine what a burglar might do to break into a house and then turn that action into the circuit switch. For example, an intruder might break through a window so that you could make the glass itself a circuit. The easiest way to do this is to run a current through a thin line of foil wire affixed to the surface of the glass. If a burglar breaks the glass, the circuit is broken, and the alarm is triggered.
Floor mats are another simple option. An essential floor mat uses an open circuit design with two metal strips spaced apart. When somebody steps on the mat, the pressure pushes the two metal strips together, completing a circuit.
These circuit systems are best for guarding the perimeter of a house or business -- the points an intruder would enter the building. In the next section, we'll look at systems that detect an intruder once they have already made it inside.
Circuit alarms are very effective for guarding the perimeter of a house, but they don't work so well inside a building. This is because the intruder's actions are highly unpredictable -- you don't know where they'll go or what they'll touch. A specific "trigger" isn't very effective. To detect an intruder who's already in the house, you need a motion detector.
Essential motion detectors are relatively common these days. You see them all the time in automatic doors, for example. There are several different sorts of sensors.
An automatic door opener is an example of a radar-based motion detector. The box above the door sends out bursts of microwave radio energy (or ultrasonic sound waves) and then waits for the reflected energy to bounce back. If there is nobody in front of the door, the radio energy will bounce back in the same pattern. But if somebody enters the area, the reflection pattern is disturbed. When this happens, the sensor sends a signal, and the door opens. In a security system, the sensor sends an alarm signal when the reflection pattern in a room is disturbed.
If somebody disturbs the reflection pattern, the motion detector sends an alarm signal to the control box.
Another simple design is a photo-sensor motion detector. These are the devices you might see in a store at a shopping mall. When somebody enters the store, the motion detector sounds like a chime or bell. Photo-sensors have two components:
- a source of focused light (often a laser beam)
- a light sensor
In a home security system, you aim the beam at the light sensor across a passageway in your house. When somebody walks between the light source and the sensor, the beam's path is blocked briefly. The sensor registers a drop in light levels and sends a signal to the control box.
More advanced security systems include passive infrared (PIR) motion detectors. These sensors "see" the infrared energy emitted by an intruder's body heat. When an intruder walks into the field of view of the detector, the sensor detects a sharp increase in infrared energy. Of course, there will always be gradual fluctuation of heat energy in an area, so PIR detectors are designed to trigger the alarm only when infrared energy levels change very rapidly. See this page for details.
All these motion detector designs can be combined in a house to offer complete coverage. In a typical security system, the control box will not sound the alarm immediately when the motion detectors are triggered. There is a short delay to give the homeowner time to enter a security code that turns the system off.
If the security code is not entered, however, the control box will activate various alarms. In the next section, we'll look at some of the alarm types you might find in a typical security system.
Sounding the Alarm
There are several things a security system might do when it detects an intruder. In an advanced technique, the control box will be wired to several different components. Typically, it will activate:
- a siren or other loud alarm noise
- flashing outdoor lights
- a telephone auto-dialer
The siren and lights serve three functions:
- They alert occupants and neighbours that someone has broken into the house.
- They drive the intruder away.
- They signal to the police which house has been broken into.
The telephone auto-dialer can:
- Dial the police directly, and play a pre-recorded message giving the address of the house and any other relevant information. This message will usually play repeatedly so that the police will still hear it even if the call is put on hold for some time.
- Dial the security company that installed the equipment. In this case, the control box can feed specific information about the intrusion -- which circuits or motion detectors were activated, etc. The security company then relays this information to the police.
Home security is a rapidly growing field, and new and improved burglar alarms popping up all the time. For the most part, these systems are all built around the same basic structure. A central control box monitors several motion detectors and perimeter guards and sounds an alarm when any of them are triggered.
To find out about specific alarm devices and new installation techniques, check out the sites listed on the next page, or talk to a security system installer in your area.
What Does The Control Panel Do?
The circuit and sensor's alarm system are monitored by the control panel – the computer that arms the security system and detects breaks in the electric circuit. This control panel has its power supply, so the burglar cannot cut off the power before breaching the perimeter.
When the circuit is broken, the Control Panel will either sound an audible alarm or alert the security company – in some cases, both.
The Control Panel is integrated with a touchpad or touchscreen, where the alarm can be armed and disarmed. Usually, the only way to turn off the audible alarm is by punching the alarm's PIN into the touchpad.
Note that the panel and the touchpad are not necessarily in the same place; the board is often hidden in an out-of-the-way space to make it harder for burglars to find and disable.
Verify Alarms at Central Alarm Panel
A burglar alarm system may have several keypads strategically located throughout the protected buildings. These keypads allow authorised users to arm and disarm the alarm system, as well as report on the overall system status.
However, there will always be that central control panel—the on-site "brains" of the installed security system—that evaluates incoming alarms. It processes the event to determine whether incoming alarms are "false" alarms that the system should ignore or "verified" alarms that indicate the presence of an intruder.
Maintaining Your Burglar Alarm
Regular maintenance will highlight and reduce issues, giving you peace of mind. With a burglar alarm maintenance contract from Fire Action, your alarm will be checked once a year (twice a year if you want a police monitoring contract).
With us, professionally maintaining your system can help tackle any problems with false alarms. It is also a requirement of some insurance companies if you want a monitoring contract in place.