Burglar alarm systems have sensors that are connected to a central control unit. The sensors are activated as needed. When they are active, if they detect a condition that could indicate a security problem, they notify the control unit. The control looks at the global pattern of which sensors are signalling what, and determines if there is a significant probability of a real problem. If so, it will raise an alarm, either locally, or at a centralized security station.
Indoor motion, or the presence of an unexpected person, can be detected in a number of different ways. The body heat of a person can trip a passive infrared detector. Emission fields are generated by microwave and ultrasonic sensors. Movement within the field changes it in a detectable way.
Breaking glass often indicates some sort of problem. Glass break detectors can sense the unique sound pattern associated with this. Some burglary alarm systems can detect threats other than burglary. Smoke, heat, or carbon monoxide detectors may detect a fire or carbon monoxide from a malfunctioning appliance.
Most home systems primarily use indoor sensors. A number of types of outdoor sensors are also available. Some of them are based on the technologies used for indoor systems. The usually sense efforts to go over or through a wall or a fence.
The sensors need to be able to talk to the control unit. Either wired or wireless technology may be used. Of course wired connections require running wires, but they do cover the power needs of the sensors. Wires can be cut. If there are frequent health check messages between the control and the sensors, cut wires can be detected and can trigger alarms.
Wireless connections are easier to set up. They may or may not be easy to disrupt, depending on the specific technology used. They generally require more technical sophistication to disrupt. With wireless system, power must be provisioned for the sensors, either via connection to line power or via batteries.
The control unit must inform someone via an alarm when there is a problem. A flashing light or a sound such as a siren, voice, or buzzer will do the job locally. There may be a private line to a security center, or the public phone network or a wireless interface may be used for the central alarm. The signal may go to an alarm company security center, or it may go to the police. Some areas have banned direct connection to a police station.
There must be simple methods for activating or deactivating the system at different times of day. There might be separate modes for everybody home, everybody gone, and nighttime everybody in bed. It must be configurable as well. Usually the system will be activated by the last person to leave and deactivated by the first person in.
Those are some basics of burglar alarm systems. They can be a little complex, but they are often worth the investment needed to buy them, install them, and learn how to use them. Once they are running they should make you more secure with little or no impact on how you do things.
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