How Alarm Systems Work

Alarm Sensors

The most basic component of an alarm system are the alarm sensors themselves. These sensors are placed on all protected doorways, windows and other entryways, designed to trigger the alarm when the door or window is opened. The majority of alarm sensors feature two parts. One of these contains a small magnet; the other contains a circuit with a metal switch that the magnet holds closed. When the door or window is opened, the magnet can no longer hold the circuit closed and the flow of electricity through the circuit is broken (triggering the alarm.) This type of alarm system is the most common, since a break in the flow of electricity will set off the alarm. This prevents intruders from being able to cut the wires attached to the sensors in an attempt to disable the alarm.

Some alarm systems also feature motion detectors. These detectors generally use radio waves to map the area they observe, receiving back an echo of the pulses they send out. Should an intruder enter the area that the motion detector is monitoring, it interrupts the return of the echo. This interruption signals the system that something has entered the area that wasn't there previously. Some motion detectors also incorporate infrared scanners, allowing them to detect sudden increases in heat (such as the body heat that would be generated by an intruder) as a means to activate the alarm.

Because alarm system components rely on electricity to operate, it's important that the systems aren't affected by power outages. Alarm systems have their own battery power sources, ensuring they will operate even if power to the main building is cut off. The majority of alarm systems feature rechargeable batteries that are plugged in to constantly charge when power is present. This ensures that they'll be fully charged should the power drop out, and also ensures they'll begin charging again as soon as power has been restored.

One of the most important parts of an alarm system is the control panel, which is generally the "brain" of the alarm system. Because many homeowners and businesses only use their alarm systems when no one is present, it would be very difficult to arm and disarm the alarm without having a control panel to tell who was authorized to go in and out from who wasn't. Setting off an active alarm sensor lets the control panel know that someone has entered, causing it to begin counting down on a timer. If a pass code isn't entered on the control panel, the alarms will activate. Most control panels are designed to detect the difference between a forceful entry and a peaceful one, allowing the alarm to respond differently to an authorized user entering and a break-in.

The most basic alarm systems have an audible alarm that's activated when an unauthorized entry is made, but a number of alarm systems are also monitored by a central alarm monitoring service. This monitoring service acts as a "silent alarm," with the alarm also dialing in to alert the service that the alarm has been activated. The service will then contact the police or other emergency services so they can respond to the cause of the alarm much faster than if the home or business owner called them.