Burglar Alarm

A burglar alarm is a system that detects the presence of an intruder and gives an alarm. If the primary aim is to deter intruders, a bell, horn, siren, or light is used to give the alarm; if the primary aim is to apprehend intruders, a signal is transmitted by wire to a nearby police station or security office.

An electrical alarm system has circuits with pushbutton switches whose contacts are closed by the closing of doors and windows. When a door or window is opened, the switch contacts open and activate the alarm.

Photo by Ove Topfer
Photo by Ove Topfer

An infrared alarm system uses an infrared beam projected onto a photoelectric cell either directly or by means of mirrors. If an intruder interrupts the invisible infrared beam, the break is detected, triggering the alarm. A wide area can be covered when the beam is deflected by mirrors.

An electronic alarm system has two balanced electronic oscillators connected to an antenna mounted in the area to be protected. The presence of an intruder near the antenna causes the oscillators to become unbalanced because of his body capacitance; the unbalance is detected, triggering the alarm.

An ultrasonic alarm system constantly transmits and receives an ultrasonic wave pattern; any movement of an intruder causes the pattern of the received signal to differ from that of the transmitted signal; this difference is detected and used to trigger the alarm.

More by this Author

  • Termites
    0

    Termites are any of a group of small social insects that feed primarily on wood. Although termites are often called white ants, they are not related to ants. They form a separate order, the Isoptera, and are related to...

  • Bricks & Tiles
    0

    Bricks and tiles are construction materials usually made by mixing finely ground clay or shale with water and firing, or baking, the mixture. Bricks may be solid or pierced with holes. They range in color from a burned...

  • Everything You Ever Wanted To Know About Poop
    21

    Poop aka Stools aka Feces. This is the term applied to the discharges from the bowel. They are also referred to as "motions."


Comments

No comments yet.

    Sign in or sign up and post using a HubPages Network account.

    0 of 8192 characters used
    Post Comment

    No HTML is allowed in comments, but URLs will be hyperlinked. Comments are not for promoting your articles or other sites.


    Click to Rate This Article
    working