Burglar (or intrusion), fire and safety alarms are found
in electronic form today. Sensors are connected to a control unit via either a
low-voltage hardwire or narrowband 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 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
(i.e., "car alarms"). See also fire alarm control panel for specific fire system
issues. Burglar alarms are sometimes referred to as alarm systems, see burglar
alarm control panel for a discussion of hard-wired burglar alarm system design.
System Connections
The trigger signal from each sensor is transmitted to one or more control unit(s)
either through wires or wireless means (radio, line carrier, infrared). Wired
systems are convenient when sensors (such as smoke detectors) require power to
operate correctly, however, they may be more costly to install. Entry-level
wired systems utilize a Star network topology, where the panel is at the center
logically, and all devices "home run" its wire back to the panel. More complex
panels use a Bus network topology where the wire basically is a data loop around
the perimeter of the facility, and has "drops" for the sensor devices which must
include a unique device identifier integrated into the sensor device itself.
Wired systems also have the advantage, if wired properly, of detecting tampering
with the wiring connections. Wireless systems, on the other hand, often use
battery-powered transmitters which are easier to install, but may reduce the
reliability of the system if the sensors are not supervised, or the batteries
maintained. Depending on distance, construction materials, or one or more
wireless repeaters may be required to get the signal reliably back to the alarm
panel. Hybrid systems utilize both wired and wireless sensors to achieve the
benefits of both. Transmitters, or sensors can also be connected through the
premises electrical circuits to transmit coded signals to the control unit (line
carrier). The control unit usually has a separate channel or zone for burglar
and fire sensors, and better systems have a separate zone for every different
sensor, as well as internal "trouble" indicators (mains power loss, low battery,
wire broken, etc).
Alarm Connection and Monitoring
The desired result of an alarm system is to cause an appropriate alarm output
and response when the sensors indicate the valid conditions for triggering of
the alarm. The ability of the panel to communicate back to the Monitoring Center
is crucial to the concept of monitoring, and it is often overlooked or down
played.
Depending upon the application, the alarm output may be local or remote or a
combination. Local alarms do not include monitoring, though may include indoor
and/or outdoor sounders (e.g. motorized bell or electronic siren) and lights
(e.g. strobe light) which may be useful for signalling an evacuation notice for
people during fire alarms, or where one hopes to scare off an amateur burglar
quickly. However, with the widespread use of alarm systems (especially in cars),
false alarms are very frequent and many urbanites tend to ignore alarms rather
than investigating, let alone contacting the necessary authorities. In short,
there may be no response at all. In rural areas (e.g., where nobody will hear
the fire bell or burglar siren) lights or sounds may not make much difference
anyway, as the nearest responders could take so long to get there that nothing
can be done to avoid losses.
Remote alarm systems are used to connect the control unit to a predetermined
monitor of some sort, and they come in many different configurations. High-end
systems connect to a central station or responder (eg. Police/ Fire/ Medical)
via a direct phone wire (or tamper-resistant fiber optic cable), and the alarm
monitoring includes not only the sensors, but also the communication wire
itself. While direct phone circuits are still available in some areas from phone
companies, because of their high cost they are becoming uncommon. Direct
connections are now most usually seen only in Federal, State, and Local
Government buildings, or on a school campus that has a dedicated security,
police, fire, or emergency medical department. More typical systems incorporate
a digital telephone dialer unit that will dial a central station (or some other
location) via the Public Switched Telephone Network (PSTN) and raise the alarm,
either with a synthesized voice or increasingly via an encoded message string
that the central station decodes. These may connect to the regular phone system
on the system side of the demarcation point, but typically connect on the
customer side ahead of all phones within the monitored premises so that the
alarm system can seize the line by cutting-off any active calls and call the
monitoring company if needed. Encoders can be programmed to indicate which
specific sensor was triggered, and monitors can show the physical location (or
"zone") of the sensor on a list or even a map of the protected premises, which
can make the resulting response more effective. For example, a water-flow alarm,
coupled with a flame detector in the same area is a more reliable indication of
an actual fire than just one or the other sensor indication by itself. Many
alarm panels are equipped with a backup dialer capability for use when the
primary PSTN circuit is not functioning. The redundant dialer may be connected
to a second phone line, or a specialized encoded cellular phone, radio, or
internet interface device to bypass the PSTN entirely, to thwart intentional
tampering with the phone line(s). Just the fact that someone tampered with the
line could trigger a supervisory alarm via the radio network, giving early
warning of an imminent problem (e.g., arson). In some cases a remote building
may not have PSTN phone service, and the cost of trenching and running a direct
line may be prohibitive. It is possible to use a wireless cellular or radio
device as the primary communication method. There is controversy within the
alarm industry as to the usage of the Internet as a primary signalling method,
due to the twin issues of the immediacy and urgency of an alarm signal, and the
lack of quality of service within the current design of the public internet.
Monitored alarms and speaker phones allow for the central station to speak with
the homeowner and/or intruder. This may be beneficial to the owner for medical
emergencies. For actual break-ins, the speaker phones allow the central station
to urge the intruder to cease and desist as response units have been dispatched.
The list of services to be monitored at a Central Station has expanded over the
past few years to include: Intrusion Alarm Monitoring; Fire Alarm & Sprinkler
Monitoring; Critical Condition Monitoring; Medical Response Monitoring; Elevator
Telephone Monitoring; Hold-Up or Panic Alarm Monitoring; Duress Monitoring; Auto
Dialer tests; Open & Close Signal Tracking, or Supervision; Open & Close
Reporting; Exception Reports; and PIN or Passcode Management. Increasingly, the
Central Stations are making this information available directly to end users via
the internet and a secure log-on to view and create custom reports on these
events themselves.
Alarm Response
Depending upon the zone triggered, number and sequence of zones, time of day,
and other factors, the monitoring center can automatically initiate various
actions. They might be instructed to call the ambulance, fire department or
police department immediately, or to first call the protected premises or
property manager to try to determine if the alarm is genuine. They could also
start calling a list of phone numbers provided by the customer to contact
someone to go check on the protected premises. Some zones may trigger a call to
the local heating oil company to go check on the system, or a call to the owner
with details of which room may be getting flooded. Some alarm systems are tied
to video surveillance systems so that current video of the intrusion area can be
instantly displayed on a remote monitor, not to mention recorded.
The first video home security system was patented (patent #3,482,037) on
December 2, 1969 to Marie Brown, an African American inventor. The system used
television surveillance.
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 repairperson 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.
Fire sensors can be "isolated", meaning that when triggered, they will not
trigger the main alarm network. This is important when smoke and heat is
intentionally produced. The owners of buildings can be fined for generating
False alarms that waste the time of emergency personnel.
False/No Alarms
System reliability can be a problem when it causes nuisance alarms, false
alarms, or fails to alarm when called for. Nuisance alarms occur when an
unintended event evokes an alarm status by an otherwise properly working alarm
system. A false alarm also occurs when there is an alarm system malfunction that
results in an alarm state. In all three circumstances, the source of the problem
should be immediately found and fixed, so that responders will not lose
confidence in the alarm reports. It is easier to know when there are false
alarms, because the system is designed to react to that condition. Failure
alarms are more troublesome because they usually require periodic testing to
make sure the sensors are working and that the correct signals are getting
through to the monitor. Some systems are designed to detect problems internally,
such as batteries going flat, connections come loose, phone circuit dead, etc.
While earlier nuisance alarms could be set off by small disturbances, like
insects or pets, newer model alarms have technology to measure the size/weight
of the object causing the disturbance, and thus are able to decide how serious
the threat is, especially useful in burglar alarms.
Independent Certification
Some insurance companies and local agencies require that alarm systems be
installed to code or be certified by an independent third party. Independent
certification insures a system meets a level of criteria above and beyond what a
sales representative may offer. This insures you have a system that will be
reliable when needed. 3rd party alarm certifying agencies include:
your local fire department
Your building department
(UL) Underwriters Laboratories
(NFPA) National Fire Protection Association
(NEC) National Electrical Code
(NFBAA) National Fire & Burglar Alarm Association
(CSAA) Central Station Alarm Association
NSI National Security Inspectorate (UK Market)
BAFE fire alarms (UK Market)
The fire department & building department set standards and inspect as needed.
U.L is the only certification enity. The other associations set guidelines.
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