What is it?
A burglar alarm system creates an invisible safety perimeter. Industry insiders call it “Intrusion Detection.” In the US we have about four burglaries every minute which translate to one every 14 seconds. It’s very common for criminals to revisit the same place more than once. If you are home during a burglary, your system can let you know immediately that the perimeter has been breached. If you are away from home, your central station monitoring service can call you to let you find out when an alarm happens.
How Does it Work?
Sensing devices like door contacts and motion detectors are placed around the perimeter and interior of the home or building to be protected. At least one keypad is mounted on the wall near a main entry/exit point. Users enter a four-digit code on the keypad to “Arm” the system. While the system is armed, it will detect any breach in the perimeter and send an alarm signal to a central station monitoring service (subscription required). At the central station, a dispatcher reviews the message and makes contact with the police to notify them of the break in.
Devices & Functions
Burglar alarms need a “brain” to tell them what to do. The control panel receives all of the signals from sensing devices and processes them. With a traditional alarm panel, all of the devices are wired back directly to a point on the board itself. New panels use wireless technology together with hard wired points or even wireless as the primary method of monitoring sensing device status. The burglar alarm panel itself is a small electronic circuit board in a brown or gray metal enclosure commonly in installed in a closet or electrical room. Inside the cabinet with the panel, there is a space for a battery or two that provide backup power in case of an outage. Some brands and models incorporate the panel and small battery into the keypad.
The keypad is where the end-user directly interacts with the system. Keypads are placed at entry/exit points to make it convenient to arm and disarm when leaving or returning to the premises. When the end-user leaves the premises a code is typed in at the keypad to “ARM” the system. The system begins a countdown timer (usually 60 seconds) to provide enough time to exit the location physically. At the end of the countdown the system is armed. Upon return when the entry or exit door is opened the countdown timer begins again. The code must be re-entered at the keypad before the timer runs out to “DISARM” the system.
Door or Window Contact
The door/window contact, or position switch, let’s the panel know if the door/window is open or closed. There are many variations, sizes, and shapes. Contacts can be installed inside door frame or on the surface for a quick and inexpensive solution. The magnet is placed on the door and should meet up perfectly with the contact when the door is closed. When the contact and the magnet line up an electrical circuit is created. When they’re separated the circuit is broken.
Motion sensors can be mounted on ceilings, walls, and corners. Many types of “motions” emit a signal into the monitored environment to detect movement. Some of the technologies that provide this kind of detection are, Tomographic (radio), Ultrasonic (sound), Microwave (radar), and by far the most widely used Passive Infrared (PIR). PIR’s do not send energy out to receive signals in return. They use a passive technology that is sensitive to skin temperature.
Glass beaks are specialized detectors that use a microphone to pick up the sounds of breaking glass. Most models have a sensitivity setting to allow for fine tuning. This kind of detection is very useful near glass storefronts or any area with a large number of windows.
Siren and Bell
Every intrusion detection system needs a siren or bell on the exterior of the building. When the system goes into alarm, the loud noise should send the burglar running. The bell will also draw the attention of anyone nearby increasing the odds of crime intervention and first responder notification. In smaller buildings and homes the sound made by the keypad during an alarm is enough to achieve the same effect inside the premises. For larger areas, an inside siren can be installed to make a big sound in the event of an alarm.