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 is used to interact with a response device. 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 ,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 (that is, "car alarms"). Burglar alarms are sometimes referred to as alarm systems.
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, remote, or a combination. Local alarms do not include monitoring, though may include indoor and/or outdoor sounders (such as motorized bell or electronic siren) and lights (e.g. strobe light) which may be useful for signaling 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 (that is, 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 (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. 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 signaling 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.
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 an ambulance, the 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 who would then 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, and 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. 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 a furnace servicer 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 low or dead batteries, loose connections, phone circuit trouble, 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, which is especially useful in burglar alarms.
System connections: technical details
The trigger signal from each sensor is transmitted to one or more control units, 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 both, 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).
Some insurance companies and local agencies require that alarm systems be installed to code or be certified by an independent third party. Independent certification ensures a system meets a level of criteria above and beyond what a sales representative may offer. This insures clients have a system that will be reliable when needed. Third-party alarm certifying agencies include the local fire department, the building department, Underwriters Laboratories (UL), National Fire Protection Association (NFPA), and the National Fire & Burglar Alarm Association (NFBAA). (The fire department and building department set standards and inspect as needed. UL is the only certification entity. Other associations set guidelines.)
- Schatz, David A., et al. Video Safety Curtain. U.S. Patent No. 6,297,844, Issued Oct. 2, 2001.
- Trimmer, H. William. Understanding and Servicing Alarm Systems. Stoneham: Butterworth. 1981. ISBN 0409950459
- Walker, Philip. Electronic Security Systems: better Ways to Crime Prevention. Cambridge, UK: University Press. 1985. ISBN 0408011602
- Weber, Thad L. Alarm Systems and Theft Protection (2d ed). Stoneham: Butterworth. 1985. ISBN 0913708119
All links retrieved September 13, 2012.
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