February 11, 2009

Design your own burglar alarm; prevent the theif

A simple sound activated burglar alarm system

Burglar alarm

Burglar (or intrusion), fire and safety alarms are found in electronic form to-
day. Sensors are connected to a control unit via either a low-voltage hardware
or narrow band RF signal, which in turn connects to a means for announcing
the alarm, hopefully to elicit some response. The most common security sensors indicate the opening of a door or window or detect motion via passive
infrared (PIR). In new construction systems are predominately hardwired
for economy while in retrofits wireless systems may be more economical and
certainly quicker to install. Some systems are dedicated to one mission, others handle fire, intrusion, and safety alarms simultaneously. Sophistication
ranges from small, self-contained noisemakers, to complicated, multi-zoned
digital systems with color-coded computer monitor outputs. Many of these
concepts also apply to portable alarms for protecting cars, trucks or other
vehicles and their contents.

Access Control

Access Control and Bypass Codes To be useful, an intrusion alarm system is
deactivated or reconfigured when authorized personnel are present. Authorization may be indicated in any number of ways, often with keys or codes
used at the control panel or a remote panel near an entry. High-security
alarms may require multiple codes, or a fingerprint, badge, hand-geometry,
retinal scan, encrypted response generator, or other means that are deemed
sufficiently secure for the purpose. Failed authorizations should result in an
alarm or at least a timed lockout to prevent "experimenting" with possible
codes. Some systems can be configured to permit deactivation of individual
sensors or groups. Others can also be programmed to bypass or ignore individual sensors (once or multiple times) and leave the remainder of the system
armed. This feature is useful for permitting a single door to be opened and
closed before the alarm is armed, or to permit a person to leave, but not
return. High-end systems allow multiple access codes, and may even permit
them to be used only once, or on particular days, or only in combination with
other users' codes (i.e., escorted). In any case, a remote monitoring center
should arrange an oral code to be provided by an authorized person in case
of false alarms, so the monitoring center can be assured that a further alarm
response is unnecessary. As with access codes, there can also be a hierarchy
of oral codes, say, for furnace repair person to enter the kitchen and basement sensor areas but not the silver vault in the butler's pantry. There are
also systems that permit a "duress" code to be entered and silence the local
alarm, but still trigger the remote alarm to summon the police to a robbery.