Burglar Alarm Systems. Info on fire and burglar alarm systems, links to Burglar Alarm Systems.

Burglar alarms can be separated into two categories, perimeter alarms for guarding entry points such as doors and windows and internal sensors for detecting intruders within the secured area.

Perimeter alarms

Perimeter alarms detect changes in secured access points, ie the opening of a door or the smashing of a window. A secure perimeter will have alarms on every point of access. Some alarms can be set up to sound in the event of a door or window opening, and these are generally simple switches mounted on the frames which open or close electronic circuits. Other alarms are placed on window glass and open a circuit in the event of the glass breaking.

Internal alarms

Internal alarms come in several main types, motion sensors, light beams and infra red heat sensors being most common. A light beam is set up to emit a laser which is detected by a sensor, usually across a passageway. If an object, such as an intruder, passes between the emitter and the sensor, the beam is interrupted, triggering an alarm. Motion sensors and heat sensors have similar uses, as both are set up to 'watch' an area for intruders. Motion sensors detect movement in the secured area by emitting radio waves and sounding the alarm if the returning reflection pattern changes, indicating a change in the state of the secured area. Infra red heat sensors detect heat in their area, and sound the alarm if there is a sudden increase in infra red radiation, indicating something warm in the area.

Alarms

Most often an alarm will be a loud noise, designed to alert people close by to the triggering of a sensor, but other types of alarm are possible. A silent, visual alarm can alert others while leaving the intruder unaware he has been discovered. Some systems can be set up to auto-dial a phone system to alert persons at a remote location, such as the nearest police station, to the presence of an intruder.