are primarily installed to detect and report unauthorized entry into a
protected location. In general, the design characteristics are typically
intended to provide for the ability to detect the opening of selected
doors and windows, detect unauthorized or unapproved motion within the
protected environment and/or detect a forced attack against structural
materials such as glass, wood, metal or concrete.
system consists of three basic components - Sensors, a Control and Annunciation
equipment. The sensors initiate an alarm, the control directs per-programmed
system actions and the annunciation equipment warns, or sets forth a visual
and/or audible alert which is intended to alert neighbors or monitoring
personnel there is cause for concern. All three component parts can be
connected by wire, a radio frequency link or a combination of both.
a pre-programmed response to sensor activation(s), a control panel manages
the prompts necessary to turn the system on or off. In addition, it provides
the ability to switch to battery back up power in case of a commercial
power failure. If the system is designed, installed and maintained properly,
an intruder's attempt at an unauthorized, unlawful or forced attempt at
entry should theoretically be detected.
the desire is to detect and report at the onset of the attempted intrusion
- In theory, prior to an actual penetration of the protected area. Short
of this early notification, an intrusion must be recognized after the
fact as unauthorized or undesired movement/motion or noise within the
protected location. These occurrences and the ensuing report are a direct
result of detector capabilities, design criteria, and decisions relating
to sensor placement and positioning. Report of unauthorized activity may
be the result of an attempt to gain entry from the outside, or as in the
case of a "stay-behind", a report may be initiated upon an intruder attempting
to leave. In either case, with a properly designed system, system sensors
should respond to abnormal or undesired activity and a "cry for help"
should be initiated.
It is the
"cry for help" that is most important in any alarm system. Without the
ability to provide notification of unwanted or undesirable activities
and the details surrounding a particular event, the detection capabilities
an investigation where an intrusion detection system (burglar alarm) is
evident, it is important to first note the system's condition. This is
accomplished by a survey and it should be conducted at the onset of the
investigation. This survey should ultimately determine a system's design
characteristics (strengths and weaknesses) and whether there is any evidence
and design technology should be understood as they are recognized. Although
intended to detect human actions and movement, some sensors also have
the potential to detect physical phenomena or respond to changes in the
environment that are not necessarily intruder related.
infrared motion sensors operate on the principle that they will detect
intruder movement because a human being passing in view of the sensor
will introduce changes or new levels of infrared energy in certain pre-selected
monitor points. This change in temperature, or recognition of a difference
from the norm in one sensor viewing area to another, because of an intruder
passing between the sensor and the reference point, is "interpreted" as
motion for purposes of detecting an intruder. Significant changes in temperature
levels or a sudden rise in infrared energy are, however, not exclusive
to just those produced by a burglar.
Do not assume
that features available in one manufacturer's model of control are the
same as that of another manufacturer, even if they may have the same appellations,
physical resemblance or labeling style and colors. Do not assume a particular
brand or model of control is always intended to operate the same in all
installations. Some features may be options or "add-ons". In addition,
do not take for granted that a premise owner understands all the operational
aspects of their system. It is not uncommon to find that some system features
are not even known by a user.
are not designed to be operated by a unique individual. They are designed
to operate solely on criteria established by equipment manufacturer's,
system installers and system designers. There is no such thing as a universal
alarm system. Moreover, there are too many different equipment manufacturers
and system options to allow for assumptions.
should immediately be taken under advisement when conducting an investigation
where a burglar alarm system has been installed are as follows:
upon arrival? Are indicator lights on, off, flashing, or steady? What
are the colors of the lights that are on? Are there any messages on
a keypad screen? If there is a lock, used to turn the system on or off,
what is the position of the keyway?
sensor technologies are employed (e.g. magnetic switches, glass break
detectors, passive infrared motion sensors, floor mats, photoelectric
- Are there
any sensors that do not appear to be connected to the control panel
(e.g. wires disconnected, batteries missing, transformers unplugged)?
- What is
the extent or area of sensor coverage?
is location of alarm control panel?
- How is
panel secured? Is panel in a secure area, room or closet? Is access
to panel restricted? Is panel housing door open, closed, locked, unlocked,
screwed shut, damaged, etc?
- What is
condition of alarm panel itself? Are all wires leading into or entering
the panel enclosure connected to the panel? Are all wires that appear
to leave the panel (e.g. telephone line or connection to local noisemaker)
- Is an
auxiliary battery connected to the panel? If so, what is the condition
of the battery (e.g. normal appearance, split, cracked, broken terminals,
etc.)? If disconnected, what is condition (e.g. charged, discharged
below acceptable limits, etc.)?
- What is
condition of alarm panel fuses? Is there any that have been blown? Are
- If alarm
is monitored remotely, is the telephone line connected at all access
points up to and including those outside the protected location (e.g.
interior terminal blocks, equipment closet punch blocks, ground pedestal,
telephone pole, cross box, etc.),
- If alarm
is transmitted by radio or cellular telephone, is there indication that
antenna is capable of radiating a signal? Does transmitter or cellular
telephone have power?
- If annunciation
is local, are wires to bell, strobes or siren intact? Is noisemaker
present and in good condition?
- How is
system activated or deactivated (turned on and off)? If by key, what
is resistance to manipulation and/or tampering? If keypad is used, do
authorized individuals all have same code or do they each have unique
codes? Does system report openings and closings?
- Is mechanism
to control system (keypad or switch lock) located inside or outside
the protected location? Are there built-in penalties for tampering or
attempting to spoof the system's operational features?
- In the
event system is remotely monitored, determine last report of activity
at annunciation point and circumstances surrounding transmission of
signal. Determine response procedures and if appropriate, obtain a history
of alarm activations, repairs and/or service calls for the premise in
to obtain hard copy records of work products that contain information
such as times, equipment brand names, model numbers, dates of repairs
or changes in system configuration and installer or repair personnel
the design parameters, the operation, and the reporting capabilities of
a burglar alarm system has the potential to help identify possible co-conspirators,
possibly establish a time for the activation of an incendiary device and/or
assist in determining or corroborating the location where a fire may have
started. Understanding how a burglar alarm system is intended to detect
burglars or prevent their movement without detection, may in the final
analysis, be the key element that helps to resolve some questionable aspects
in an arson investigation.