Burglar alarm

From ArticleWorld

Burglar alarm are common devices used inform about an intrusion, fire or other emergencies. Safety alarms are usually found in the electronic form today. Most burglar alarms consist of a system of sensors connected to a control unit, which is connected to a means for announcing the alarm. Some systems are dedicated to a single mission while others handle several functions like fire, intrusion, and safety alarms simultaneously. They may range from the small self-contained noisemakers, to the complicated digital systems with computer monitor outputs. They are also used in portable alarms for protecting cars, trucks or other vehicles and their contents. Burglar alarms are sometimes referred to as alarm systems. Intrusion burglar alarms are generally of two classes: point detectors and area detectors. Point detectors show an intrusion at a specific point and include mechanical or magnetic contacts on doors and windows to detect when they are opened or broken. Area detectors indicate an intruder's presence within a protected area and use such technologies as ultrasonic transducers, passive heat detectors, and microwave transducers. In general, area sensors detect a sudden change in the measurements taken and trigger at some predetermined threshold. They are, however, much more prone to false alarms than point sensors, due to improper adjustments. Sophisticated computer-aided sensors include image-processing systems to detect and filter changes in a surveillance video picture and they can be programmed to detect or ignore different types of motion in different parts of the scene, and can tell the difference between a person and moving objects. Fire alarm sensors are of three general categories: smoke, flame and heat. Smoke detectors are sensors that detect the chemical byproducts of fire by ionized conduction. Flame detectors react to the light spectrum of fire, either through infrared or ultraviolet, or both. Heat detectors react to a high temperature, or a rapid rate of temperature rise. Safety detectors include thermostats for detecting excessively high or low temperatures, water sensors for flooding, excessive carbon monoxide concentrations low oxygen concentrations, electrical current on or off, gates and valves open or closed, water pressure available in sprinkler systems. Some intrusion detectors can also be used as safety sensors as well.