Technical details of alarm systems

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Technics

Wireless Alarm Systems

Wired Alarm Systems

Video surveillance

These are the major components of a security system:

• Alarm center: The alarm center is the heart of the entire alarm system. It gets informations from the various sensors and decides if it should trigger an alarm. The alarm center may be switched to "disarmed", "armed away" and "stay armed". The alarm center detects sabotage on the sensors and reports low batteries that need to be replaced.
• Horn, Siren: Horns on the outside of a building are signalling an alarm with sound and light. It is to distinguish between wired horns, wireless controlled sirens that need a power supply and completely wireless horns that are powered by a solar panel and a rechargable battery. Wired sirens require a cable with several wires between the alarm center and the horn. Solar powered sirens need to be mounted on a place that is exposed to light. Good Horns have a rechargeable back up battery built in and are self protecting, i.e. the trigger an alarm and start to sound if they're removed from the wall. Horns are discouraging a potential criminal and should be mounted on a well visible place.
• Motion detectors divide their view in small segments and use an infrared device to recognise if an object with body temperature is moving within their view. Usually they come with a field of view of 90° and a range of a few meters, and thei're mounted head high to avoid false alarms caused by pets. Motion detectors are available  as wired and as wireless devices. Special versions with alonger range, for ceiling mount or to be used outdor are available.
• Door/Window Sensors are attached to doors and windows and trigger if the distance between a magnet and the sensor becomes too big. Usually window sensors can be mounted in a way that windows can be tiltet without trigerring an alarm. For extended security the wireless sensors can be equipped with a passive glass breaking detector.
• Light barriers are used to secure a small area. One side of the light barrier a light emitting device (usually in the invisible infrared range), the other side contains a component that is sensitive to light and sees if the beam is interrupted. To avoid false alarms caused by animals (birds) the alarm is only trigerred if two beacons are interrupted at the same time. Light barriers are mounted in a way that nobody can jump over or crawl under the beacons.
• Fire detectors are connected to the alarm center and trigger an alarm if the temperature goes above a certain level .
• Smoke detectors contain a miniaturised light barrier that triggers when the sight is limited by smoke.
• Water detectors have a sensor that triggers when it gets wet.
• Panic buttons are used to call for help when threatened. The alarm can be with sound or silent using only the phone. Panic buttons are available for the wrist, to be carried around the neck or wall mounted.
• Voice dialer are used to transmit an alarm or a status message to the police, a security service or a trusted person. A prerecorded message will be transmitted. Voice dialer are connected to a land line or they use a GSM service.
• Key Fob Transmitterare miniaturised transmitters to arm or disarm the security system. Additionally key fob transmitter can be used to start a panic alarm. The range of such transmitters is limited to a few meters.

Features of a modern alarm system:

• "armed away": All sensors that may detect a burglar are activ and may trigger an alarm.
• "armed at home": The sensors perimeter of the protected object trigger an alarm, detectors inside the building (usually the motion detectors) don't. The alarm system is armed, but people inside the house can move freely.
• "disarmed"means all windows and doors can be opened, and people can move inside the house without starting an alarm. Smoke detectors, panic buttons and sabotage attempts are still causing an alarm.
• People supervision is used to monitor aged are weak peorsons. An informative call is startet when the supervised person has noot moved within some hours.
• Emergency call: Other than a burglar alarm an emergency call is started manually by a person. The alarm center sends a differen message and the police or security center knows that a person is threatened and can act accordingly.