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How Alarm Systems Work


Home and business security alarm systems typically consist of three main parts that are designed to detect, determine and deter criminal activity or other life safety situations. An alarm system can detect an event such as a home invasion, fire, or other environmental change; determine if the event presents a danger; and then send a notification about the event to a central monitoring station.

how security systems work


The part of an alarm system that detects activity is called a sensor. Below are several types of sensors that may be used to protect your home or business.

Door and Window contacts are generally magnetic switches that sense the opening or closing of a door or window. The contact is attached to a door or window and the switch is held closed by a magnet mounted to the frame. When the door or window moves away from the magnet, the switch opens and sends a signal to the alarm’s control panel.

Motion Detectors are used to sense the movement of people, animals, or other objects and are ideal for securing large rooms. Strictly speaking, motion detectors do not detect motion but rather sense rapid changes in temperature, such as a human passing back and forth in front of the sensor.

Glassbreak Detectors are designed to continually listen for the sound of breaking glass. When the sensor hears shattering glass, it sends an electronic signal to the alarm control panel.

Keypads are devices that are used to arm and disarm an alarm system as well as send panic signals – police, fire, and medical – to the alarm’s control panel.

Smoke Detectors are designed to detect both flaming fires with very little smoke as well as smoldering fires that produce large amounts of smoke.

Shock Sensors can detect an intruder that is using force to pound through a wall, roof, window or other area of the home or business.

Panic Buttons can send an immediate call for help – either audible or silent – upon the press of a button.

Environmental Sensors range in functionality and are designed to react to the presence of water, increases or decreases in room temperature, and carbon monoxide emissions.


The alarm system’s control panel is the brain of the system. The control panel carries out the alarm system’s decision making by processing the information it receives from various sensors and determining what action needs to be executed. For example, if a door is opened while the alarm system is disarmed, the control panel disregards the event but if a door is opened while the alarm system is armed, it will respond by sending a signal to your alarm monitoring center and triggering an alarm siren.

Alarm system control panels have built-in communicators that transmit and receive signals through phone lines, cellular devices, or internet connections. These signals are sent to a central alarm monitoring center where trained dispatchers monitor alarm system signals. In the event of an alarm, a dispatcher will contact you to verify the emergency situation and if necessary, contact the police, fire department, or EMS on your behalf.


An alarm system’s control panel responds to a triggered alarm by activating audible sirens and/or strobe lights. These devices are used to discourage criminals from further damaging your property as well as alerting you of life threatening situations such as a fire or the presence of carbon monoxide. Using yard signs and window stickers that indicate the presence of an alarm system are also proven deterrents to potential thieves.

Knowing how one works is half the battle to securing your home. The other half is designing the system of sensors, control panels, and deterrents that work for you. Start building your system now using our home security assessment.