How does a standard home alarm work?

Before we start dissecting the complexities of a home security system, please make sure you have your dictionary, electrical engineer's guide, a full pot of coffee, and about seven hours of free time.

Okay, now that we have the sarcasm aside, let's get real. Out of all the safety devices you'll ever encounter, a home alarm system is surprisingly one of the simplest. From the most basic door chime to the most complex video and motion-monitoring systems, all alarms systems are built upon the same basic foundation. So, put the engineer's guide away and get ready to have a much deeper understanding of alarms in about ten minutes.

Home Security Systems 101
Every single alarm system has two key components. First is the power supply that keeps a steady electric current flowing through the system's circuit. Some systems get this power from a battery source, which is less reliable due to the limited-life nature of batteries. Others get power from a hard-line electric source like an electrical outlet, which provides a constant current. The second main component of all alarm systems is a sensor within the circuit that can interrupt the flow of electricity.

Circuit Breaking
Think of your home alarm system as a complete circle of happily flowing electrical current. You can even make an invisible circle in the air with your finger-come on; don't be shy. Now, with your other hand, place a different finger in the path of the circle until your two fingers touch. Oops. What happened? Your finger stopped, didn't it?

This might be elementary, but it paints a good picture of how an alarm system is triggered to then send out a distress signal. When your finger was circling, that represented the system as active. The other finger cutting the circle off represented an interruption in the flow of electricity. Sensors that are typically magnets, buttons, or switches recognize this interruption, or break.

In a home alarm system, there are several areas where the electrical circuit can be broken, such as doorways and windows. When closed, two sensors meet and allow a constant flow of electricity. When opened, the sensors no longer meet and the flow is interrupted. And you guessed it; that break in the electrical flow causes an alarm to sound.

Motion Detectors
With everything explained so far, it's easy to understand how opening a window or door can trigger an alarm. But what about all that open space in the interior of the rooms? What if someone came through a window that wasn't monitored by the system's circuit? What then? That's where motion detectors come in. But don't worry; a motion detector operates on the same principles of any other sensor within the alarm system's circuit.

Attached directly into the happy flow of electricity, the motion detector sends a pulse of radar signal into an open space like your living room. Everything within this radar "picture" bounces back as a visual echo, and is recognized by the system as acceptable. Couch? Check. Television? Check. Pile of laundry? Check. It sends the same pulse several times per second, and if something else enters the picture, beep!

Although a common component to home alarm systems, motion detectors are more intended for times when no one is expected to be in the house. So, knowing this, it's probably a good idea not to wander into the kitchen for that midnight snack if your motion detectors are set.

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