A siren is a loud noise-making device. Civil defense sirens are mounted in fixed locations and used to warn of natural disasters or attacks. Sirens are used on emergency service vehicles such as ambulances, police cars, fire trucks. There are two general types: electronic. Many fire sirens serve double duty as tornado or civil defense sirens, alerting an entire community of impending danger. Most fire sirens are either mounted on the roof of a fire station or on a pole next to the fire station. Fire sirens can be mounted on or near government buildings, on tall structures such as water towers, as well as in systems where several sirens are distributed around a town for better sound coverage. Most fire sirens are single tone and mechanically driven by electric motors with a rotor attached to the shaft; some newer sirens are electronically driven speakers. Fire sirens are called "fire whistles", "fire alarms", or "fire horns". Although there is no standard signaling of fire sirens, some utilize codes to inform firefighters of the location of the fire.
Civil defense sirens used as fire sirens can produce an alternating "hi-lo" signal as the fire signal, or a slow wail as to not confuse the public with the standard civil defense signals of alert and attack. Fire sirens are tested once a day at noon and are called "noon sirens" or "noon whistles"; some time before 1799 the siren was invented by the Scottish natural philosopher John Robison. Robison's sirens were used as musical instruments. Robison's siren consisted of a stopcock that closed a pneumatic tube; the stopcock was driven by the rotation of a wheel. In 1819 an improved siren was named by Baron Charles Cagniard de la Tour. De la Tour's siren consisted of two perforated disks that were mounted coaxially at the outlet of a pneumatic tube. One disk was stationary; the rotating disk periodically interrupted the flow of air through the fixed disk. De la Tour's siren could produce sound under water, suggesting a link with the sirens of Greek mythology. Instead of disks, most modern mechanical sirens use two concentric cylinders, which have slots parallel to their length.
The inner cylinder rotates. As air under pressure flows out of the slots of the inner cylinder and escapes through the slots of the outer cylinder, the flow is periodically interrupted, creating a tone; the earliest such sirens were developed during 1877–1880 by James Douglass and George Slight of Trinity House. When commercial electric power became available, sirens were no longer driven by external sources of compressed air, but by electric motors, which generated the necessary flow of air via a simple centrifugal fan, incorporated into the siren’s inner cylinder. To direct a siren’s sound and to maximize its power output, a siren is fitted with a horn, which transforms the high-pressure sound waves in the siren to lower-pressure sound waves in the open air; the earliest way of summoning volunteer firemen to a fire was by ringing of a bell, either mounted atop the fire station, or in the belfry of a local church. As electricity became available, the first fire sirens were manufactured. In 1886 French electrical engineer Gustave Trouvé, developed a siren to announce the silent arrival of his electric boats.
Two early fire sirens were Sterling Siren. Both started manufacturing fire sirens around 1900 to 1905. Many communities have since deactivated their fire sirens as pagers became available for fire department use. During the Second World War the British civil defence used a network of sirens to alert the general population to the immanence of an air raid. A single tone denoted an "all clear". A series of tones denoted an air raid; the pneumatic siren, a free aerophone, consists of a rotating disk with holes in it, such that the material between the holes interrupts a flow of air from fixed holes on the outside of the unit. As the holes in the rotating disk alternately prevent and allow air to flow it results in alternating compressed and rarefied air pressure, i.e. sound. Such sirens can consume large amounts of energy. To reduce the energy consumption without losing sound volume, some designs of pneumatic sirens are boosted by forcing compressed air from a tank that can be refilled by a low powered compressor through the siren disk.
In United States English language usage, vehicular pneumatic sirens are sometimes referred to as mechanical or coaster sirens, to differentiate them from electronic devices. Mechanical sirens driven by an electric motor are called "electromechanical". One example is the Q2B siren sold by Federal Signal Corporation; because of its high current draw its application is limited to fire apparatus, though it has seen increasing use on type IV ambulances and rescue-squad vehicles. Its distinct tone of urgency, high sound pressure level and square sound waves account for its effectiveness. In Germany and some other European countries, the pneumatic two-tone siren consists of two sets of air horns, one high pitched and the other low pitched. An air compressor blows the air into one set of horns, it automatically switches to the other set; as this back and forth switching occurs, the sound changes tones. Its sound power
A security alarm is a system designed to detect intrusion – unauthorized entry – into a building or other area. Security alarms are used in residential, commercial and military properties for protection against burglary or property damage, as well as personal protection against intruders. Security alarms in residential areas show a correlation with decreased theft. Car alarms help protect vehicles and their contents. Prisons use security systems for control of inmates; some alarm systems serve a single purpose of burglary protection. Intrusion alarm systems may be combined with closed-circuit television surveillance systems to automatically record the activities of intruders, may interface to access control systems for electrically locked doors. Systems range from small, self-contained noisemakers, to complicated, multirally systems with computer monitoring and control, it may include two-way voice which allows communication between the panel and Monitoring station. The most basic alarm consists of one or more sensors to detect intruders, an alerting device to indicate the intrusion.
However, a typical premises security alarm employs the following components: Premises control unit, Alarm Control Panel, or panel: The "brain" of the system, it reads sensor inputs, tracks arm/disarm status, signals intrusions. In modern systems, this is one or more computer circuit boards inside a metal enclosure, along with a power supply. Sensors: Devices which detect intrusions. Sensors may be placed at the perimeter of the protected area, within it, or both. Sensors can detect intruders by a variety of methods, such as monitoring doors and windows for opening, or by monitoring unoccupied interiors for motions, vibration, or other disturbances. Alerting devices: These indicate an alarm condition. Most these are bells, and/or flashing lights. Alerting devices serve the dual purposes of warning occupants of intrusion, scaring off burglars; these devices may be used to warn occupants of a fire or smoke condition. Keypads: Small devices wall-mounted, which function as the human-machine interface to the system.
In addition to buttons, keypads feature indicator lights, a small multi-character display, or both.ect Interconnections between components. This may consist of wireless links with local power supplies. In addition to the system itself, security alarms are coupled with a monitoring service. In the event of an alarm, the premises control unit contacts a central monitoring station. Operators at the station see the signal and take appropriate action, such as contacting property owners, notifying police, or dispatching private security forces; such signals may be transmitted via telephone lines, or the internet. The hermetically sealed reed switch is a common type of two piece sensor that operates with an electrically conductive reed switch, either open or closed when under the influence of a magnetic field as in the case of proximity to the second piece which contains a magnet; when the magnet is moved away from the reed switch, the reed switch either closes or opens, again based on whether or not the design is open or closed.
This action coupled with an electric current allows an alarm control panel to detect a fault on that zone or circuit. These type of sensors are common and are found either wired directly to an alarm control panel, or they can be found in wireless door or window contacts as sub-components; the passive infrared motion detector is one of the most common sensors found in household and small business environments. It offers reliable functionality; the term passive refers to the fact that the detector does not radiate its own energy. Speaking, PIR sensors do not detect motion; as an intruder walks in front of the sensor, the temperature at that point will rise from room temperature to body temperature, back again. This quick change triggers the detection. PIR sensors may be designed to be wall- or ceiling-mounted, come in various fields of view, from narrow-point detectors to 360-degree fields. PIRs require a power supply in addition to the detection signalling circuit; the infrasound detector works by detecting sound waves at frequencies below 20 hertz.
Sounds at those frequencies are inaudible to the human ear. Due to its inherent properties, infrasound can travel distances of many hundreds of kilometers. Infrasound signals can result from volcanic eruptions, gravity waves and closing of doors, forcing windows to name a few; the entire infrasound detection system consists of the following components: a speaker as a microphone input, an order-frequency filter, an analog to digital converter, an MCU, used to analyse the recorded signal. Each time a potential intruder tries enter into a house, she or he tests whether it is closed and locked, uses tools on openings, or/and applies pressure, therefore he or she creates low-frequency sound vibrations; such actions are detected by the infrasound detector before the intruder breaks in. The primary purpose of such system is to stop burglars before they enter the house, to avoid not only theft, but vandalism; the sensitivity can be modulated depending on the size of a presence of animals. Using frequencies between 15 kHz and 75 kHz, these active detectors transmit ultras
Fire alarm notification appliance
A fire alarm notification appliance is an active fire protection component of a fire alarm system. A notification appliance may use audible, visible, or other stimuli to alert the occupants of a fire or other emergency condition requiring action. Audible appliances have been in use longer than any other method of notification. All appliances were either electromechanical horns or electric bells, which would be replaced by electronic sounders. Most of today's appliances produce sound pressure levels between 120 decibels at ten feet; the primary function of the notification appliance is to alert persons at risk. Several methods are used and documented in industry specifications published by UL. Alerting methods include: Sound ~3 kHz / ~3100 Hz tone. Used in many current notification devices. 520 Hz. Used in newer notification devices. 45 dB to 120 dB A weighted for human hearing Light 15 cd to 1000 cd candela output 1 to 2 flashes per second Coding refers to the pattern or tones a notification appliance sounds in and is controlled either by the panel or by setting jumpers or DIP switches on the notification appliances.
The majority of audible notification appliances installed prior to 1996 produced a steady sound for evacuation. In general, no common standard at that time mandated any particular tone, or pattern for audible fire alarm evacuation signals. While less common than a steady sound, differing signaling methods were used for the same purpose; these are named with respect to their distinctive structure and include, March Time, Hi-Lo, Slow-Whoop among others. Today these methods are confined to applications intended to trigger a response other than evacuation alone. In 1996, the ANSI and the NFPA recommended a standard evacuation pattern to eliminate confusion; the pattern is uniform without regard to the sound used. This pattern, used for smoke alarms, is named the Temporal-Three alarm signal referred to as "T-3" and produces an interrupted four count. CO detectors are specified to use a similar pattern using four pulses of tone. From NFPA 72, 2002 Edition: “22.214.171.124* To ensure that audible public mode signals are heard, unless otherwise permitted by 126.96.36.199 through 188.8.131.52, they shall have a sound level at least 15 dB above the average ambient sound level or 5 dB above the maximum sound level having a duration of at least 60 seconds, whichever is greater, measured 1.5 m above the floor in the occupiable area, using the A-weighted scale.”
In 1970, Space Age Electronics introduced the first visual notification appliance, the AV32 light plate and V33 remote light. Meanwhile, in 1976, Wheelock introduced the first horn/strobe notification appliances with its 700x series; the majority of visual signals throughout the 1970s and 1980s were red incandescent lights. In the 1980s, most new installations began to include visual signals, more strobes started to appear. In the United States, the 1990 Americans with Disabilities Act triggered changes in evacuation signaling methods to include the hearing impaired. Audible notification appliances would now have to include strobe lights with higher brightness intensity to alert the hearing impaired; this made incandescent lights inadequate for the purposes of the ADA. Many existing installations that did not include visual signals were retrofitted with strobe plates; these retrofit plates would allow for the easy installation of a strobe without replacing the audible signal. ADA codes required that strobes be at least 15 candelas and have a flash rate of at least 60 flashes per minute.
Companies such as Wheelock and Simplex discontinued their translucent strobes, replaced them with new, high-intensity strobes. Today, strobe synchronization is used to synchronize all strobes in a uniform flash pattern; this is to prevent individuals with photosensitive epilepsy from experiencing seizures due to unsynchronized strobes. Voice evacuation systems have become popular in most countries. Voice evacuation alarms are not as loud as horns or bells, sound an alarm tone and a voice message warning that an emergency has been reported and to evacuate the building. Voice evacuation systems can be used by personnel to give specific live information and/or instructions over the alarm system using a built-in microphone, which provides a distinct advantage over horns or bells; the system can be stand alone. In 1973, the Autocall fire alarm company manufactured the first voice evacuation system. In Europe, voice evacuation systems are a mandatory requirement for rail and air transport terminals, high-rise buildings, schools and other large facilities.
Voice systems for emergency use date back at least as far as the second world war. Following the lead of companies
Civil defense siren
A civil defence siren is a siren used to provide the emergency population warning of approaching danger, while sometimes indicating when the danger has passed. Some are used to call the volunteer fire department when they are needed. Designed to warn city dwellers of air raids in World War II, they were reused to warn of nuclear attack and of natural destructive weather patterns such as tornadoes; the generalised nature of the siren led to many of them being replaced with more specialised warnings, such as the Emergency Alert System. A mechanical siren generates sound by spinning a slotted chopper wheel to interrupt a stream of air at a regular rate. Modern sirens can develop a sound level of up to 135 decibels at 100 feet; the Chrysler air raid siren, driven by a 331-cubic-inch Chrysler Hemi gasoline engine, generates 138 dB at 100 feet away. By use of varying tones or binary patterns of sound, different alert conditions can be signalled. Electronic sirens can transmit voice announcements in addition to alert tone signals.
Siren systems may be electronically integrated into other warning systems. Many warning sirens have a sound made distinguishable from that used by emergency vehicles by the use of two simultaneous tones, with pitches in a 5:6 frequency ratio. In the United States, several sets of warning tones have been used that have varied due to age, government structure, manufacturer; the initial alerts used during World War II were the Attack Signal. The Victory Siren manual stated that when manual generation of the warbling tone was required, it could be achieved by holding the Signal switch on for 8 seconds and off for 4 seconds. In 1950, the Federal Civil Defence Administration revised the signals, naming the alert signal "red alert" and adding an "all-clear" signal, characterized by three 1-minute steady blasts, with 2 minutes of silence between the blasts. Beginning in 1952, the Bell and Lights Air Raid Warning System, developed by AT&T, was made available to provide automated transmission of an expanded set of alert signals: Red Alert Yellow Alert White Alert Blue Alert The Yellow Alert and Red Alert signals correspond to the earlier Alert Signal and Attack Signal and the early Federal Signal AR timer siren control units featured the "Take Cover" button labelled with a red background, the "Alert" button labelled with a yellow background.
AF timers changed the colour-coding, setting the Alert button as blue, the Take Cover button yellow, the Fire button red, thus confusing the colour-coding of the alerts. In 1955, the Federal Civil Defence Administration again revised the warning signals, altering them to deal with concern over nuclear fallout; the new set of signals were the Take-Cover Signal. The All-Clear signal was removed because leaving a shelter while fallout was present would prove hazardous. During World War II Britain had two warning tones: Red Warning All Clear These tones would be initialised by the Royal Observer Corps spotting Luftwaffe aircraft coming towards Britain, helped by coastal radar stations; the Attack Warning would be sounded when the Royal Observer Corps spotted enemy aircraft in the immediate area. The sirens were tested periodically; this was done by emitting the tones in reverse order, with the All Clear tone followed by the Red Warning tone. This ensured. Sirens are sometimes integrated into a warning system that links sirens with other warning media, such as the radio and TV Emergency Alert System, NOAA Weather Radio, telephone alerting systems, Reverse 911, Cable Override and wireless alerting systems in the United States and the National Public Alerting System, Alert Ready, in Canada.
This fluid approach enhances the credibility of warnings and reduces the risk of assumed false alarms by corroborating the warning messages through multiple media. The Common Alerting Protocol is a technical standard for this sort of multi-system integration. Siren installations themselves have many ways of being activated. Used are DTMF broadcasts over phone lines or over radio broadcast; this does open vulnerability for exploitation. These sirens can be tied into other networks such as a fire departments volunteer notification/paging system; the basics of this type of installation would consist of a device connected to the controller/timer system of the siren. When a page is received, the siren is activated. A mechanical siren uses a rotor and stator to chop an airstream, forced through the siren by radial vanes in the spinning rotor. An example of this type of siren is the Federal Signal 2T22, developed during the Cold War and produced from the early 1950s to the late 1980s; this particular design employs dual stators to sound each pitch.
Because the sound power output of this type of siren is the same in every direction at all times, it is described as omnidirectional. The Federal 2T22 was marketed in a 3-signal configuration known as the Federal Signal 3T22, which had capabilities for a "hi-lo" signal; some sirens, like the Federal Signal Thunderbolt series, had a blower so that more air could be pumped into the siren. While some mechanica
Physical security describes security measures that are designed to deny unauthorized access to facilities and resources and to protect personnel and property from damage or harm. Physical security involves the use of multiple layers of interdependent systems which include CCTV surveillance, security guards, protective barriers, access control protocols, many other techniques. Physical security systems for protected facilities are intended to: deter potential intruders, it is up to security designers and analysts to balance security controls against risks, taking into account the costs of specifying, testing, using, managing and maintaining the controls, along with broader issues such as aesthetics, human rights and safety, societal norms or conventions. Physical access security measures that are appropriate for a high security prison or a military site may be inappropriate in an office, a home or a vehicle, although the principles are similar; the goal of deterrence methods is to convince potential attackers that a successful attack is unlikely due to strong defenses.
The initial layer of security for a campus, office, or other physical space uses crime prevention through environmental design to deter threats. Some of the most common examples are the most basic: warning signs or window stickers, vehicle barriers, vehicle height-restrictors, restricted access points, security lighting and trenches. Physical barriers such as fences and vehicle barriers act as the outermost layer of security, they serve to prevent, or at least delay and act as a psychological deterrent by defining the perimeter of the facility and making intrusions seem more difficult. Tall fencing, topped with barbed wire, razor wire or metal spikes are emplaced on the perimeter of a property with some type of signage that warns people not to attempt to enter. However, in some facilities imposing perimeter walls/fencing will not be possible or it may be aesthetically unacceptable. Barriers are designed to defeat defined threats; this is part of building codes as well as fire codes. Apart from external threats, there are internal threats of fire, smoke migration as well as sabotage.
The National Building Code of Canada, as an example, indicates the need to defeat external explosions with the building envelope, where they are possible, such as where large electrical transformers are located close to a building. High-voltage transformer fire barriers can be examples of walls designed to defeat fire and fragmentation as a result of transformer ruptures, as well as incoming small weapons fire. Buildings may have internal barriers to defeat weapons as well as fire and heat. An example would be a counter at a police station or embassy, where the public may access a room but talk through security glass to employees in behind. If such a barrier aligns with a fire compartment as part of building code compliance multiple threats must be defeated which must be considered in the design. Another major form of deterrence that can be incorporated into the design of facilities is natural surveillance, whereby architects seek to build spaces that are more open and visible to security personnel and authorized users, so that intruders/attackers are unable to perform unauthorized activity without being seen.
An example would be decreasing the amount of dense, tall vegetation in the landscaping so that attackers cannot conceal themselves within it, or placing critical resources in areas where intruders would have to cross over a wide, open space to reach them. Security lighting is another effective form of deterrence. Intruders are less to enter well-lit areas for fear of being seen. Doors and other entrances, in particular, should be well lit to allow close observation of people entering and exiting; when lighting the grounds of a facility distributed low-intensity lighting is superior to small patches of high-intensity lighting, because the latter can have a tendency to create blind spots for security personnel and CCTV cameras. It is important to place lighting in a manner that makes it difficult to tamper with, to ensure that there is a backup power supply so that security lights will not go out if the electricity is cut off. Alarm systems can be installed to alert security personnel. Alarm systems work in tandem with physical barriers, mechanical systems, security guards, serving to trigger a response when these other forms of security have been breached.
They consist of sensors including motion sensors, contact sensors, glass break detectors. However, alarms are only useful. In the reconnaissance phase prior to an actual attack, some intruders will test the response time of security personnel to a deliberately tripped alarm system. By measuring the length of time it takes for a security team to arrive, the attacker can determine if an attack could succeed before authorities arrive to neutralize the threat. Loud audible alarms can act as a psycholo
Aesop was a Greek fabulist and storyteller credited with a number of fables now collectively known as Aesop's Fables. Although his existence remains unclear and no writings by him survive, numerous tales credited to him were gathered across the centuries and in many languages in a storytelling tradition that continues to this day. Many of the tales are characterized by animals and inanimate objects that speak, solve problems, have human characteristics. Scattered details of Aesop's life can be found in ancient sources, including Aristotle and Plutarch. An ancient literary work called The Aesop Romance tells an episodic highly fictional version of his life, including the traditional description of him as a strikingly ugly slave who by his cleverness acquires freedom and becomes an adviser to kings and city-states. Older spellings of his name have included Isope. Depictions of Aesop in popular culture over the last 2500 years have included many works of art and his appearance as a character in numerous books, films and television programs.
The name of Aesop is as known as any that has come down from Graeco-Roman antiquity it is far from certain whether a historical Aesop existed... in the latter part of the fifth century something like a coherent Aesop legend appears, Samos seems to be its home. The earliest Greek sources, including Aristotle, indicate that Aesop was born around 620 BCE in Thrace at a site on the Black Sea coast which would become the city Mesembria. A number of writers from the Roman imperial period say that he was born in Phrygia; the 3rd-century poet Callimachus called him "Aesop of Sardis," and the writer Maximus of Tyre called him "the sage of Lydia."From Aristotle and Herodotus we learn that Aesop was a slave in Samos and that his masters were first a man named Xanthus and a man named Iadmon. Plutarch tells us that Aesop had come to Delphi on a diplomatic mission from King Croesus of Lydia, that he insulted the Delphians, was sentenced to death on a trumped-up charge of temple theft, was thrown from a cliff.
Before this fatal episode, Aesop met with Periander of Corinth, where Plutarch has him dining with the Seven Sages of Greece, sitting beside his friend Solon, whom he had met in Sardis. Problems of chronological reconciliation dating the death of Aesop and the reign of Croesus led the Aesop scholar Ben Edwin Perry in 1965 to conclude that "everything in the ancient testimony about Aesop that pertains to his associations with either Croesus or with any of the so-called Seven Wise Men of Greece must be reckoned as literary fiction," and Perry dismissed Aesop's death in Delphi as legendary. Still problematic is the story by Phaedrus which has Aesop in Athens, telling the fable of the frogs who asked for a king, during the reign of Peisistratos, which occurred decades after the presumed date of Aesop's death. Along with the scattered references in the ancient sources regarding the life and death of Aesop, there is a fictional biography now called The Aesop Romance, "an anonymous work of Greek popular literature composed around the second century of our era...
Like The Alexander Romance, The Aesop Romance became a folkbook, a work that belonged to no one, the occasional writer felt free to modify as it might suit him." Multiple, sometimes contradictory, versions of this work exist. The earliest known version was composed in the 1st century CE, but the story may have circulated in different versions for centuries before it was committed to writing, certain elements can be shown to originate in the 4th century BCE. Scholars long dismissed any biographical validity in The Aesop Romance. In The Aesop Romance, Aesop is a slave of Phrygian origin on the island of Samos, ugly. At first he lacks the power of speech, but after showing kindness to a priestess of Isis, is granted by the goddess not only speech but a gift for clever storytelling, which he uses alternately to assist and confound his master, embarrassing the philosopher in front of his students and sleeping with his wife. After interpreting a portent for the people of Samos, Aesop is given his freedom and acts as an emissary between the Samians and King Croesus.
He travels to the courts of Lycurgus of Babylon and Nectanabo of Egypt – both imaginary rulers – in a section that appears to borrow from the romance of Ahiqar. The story ends with Aesop's journey to Delphi, where he angers the citizens by telling insulting fables, is sentenced to death and, after cursing the people of Delphi, is forced to jump to his death. Aesop may not have written his fables; the Aesop Romance claims that he deposited them in the library of Croesus. Scholars speculate that "there existed in the fifth century a written book containing various fables of Aesop, set in a biographical framew