An alarm device is a mechanism that gives an audible, visual or other kind of

alarm signal In animal communication, an alarm signal is an antipredator adaptation in the form of signals emitted by social animals in response to danger. Many primates and birds have elaborate alarm calls for warning conspecifics of approaching predators. ...

to alert someone to a problem or condition that requires urgent attention. Alphabetical musical instruments

Etymology

The word ''alarm'' comes from the

Old French Old French (, , ; Modern French: ) was the language spoken in most of the northern half of France from approximately the 8th to the 14th centuries. Rather than a unified language, Old French was a linkage of Romance dialects, mutually intelligib ...

''a l'arme'' meaning "to the arms", or "to the weapons", telling armed men to pick up their weapons and get ready for action because an enemy may have suddenly appeared. The word ''alarum'' is an archaic form of ''alarm''. It was sometimes used as a call to arms in the stage directions of Elizabethan dramas. The term comes from the

Italian Italian(s) may refer to: * Anything of, from, or related to the people of Italy over the centuries ** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance language *** Regional Ita ...

''all'armi'' and appears 89 times in

Shakespeare's William Shakespeare ( 26 April 1564 – 23 April 1616) was an English playwright, poet and actor. He is widely regarded as the greatest writer in the English language and the world's pre-eminent dramatist. He is often called England's nation ...

first folio ''Mr. William Shakespeare's Comedies, Histories, & Tragedies'' is a collection of plays by William Shakespeare, commonly referred to by modern scholars as the First Folio, published in 1623, about seven years after Shakespeare's death. It is cons ...

. Often explained as the off-stage sounds of conflict or disturbance, recent research suggests a bell or drum may have been used to rouse soldiers from sleep.

History and development

Early alarm devices were often

bell A bell is a directly struck idiophone percussion instrument. Most bells have the shape of a hollow cup that when struck vibrates in a single strong strike tone, with its sides forming an efficient resonator. The strike may be made by an inter ...

drums A drum kit (also called a drum set, trap set, or simply drums) is a collection of drums, cymbals, and other Percussion instrument, auxiliary percussion instruments set up to be played by one person. The player (drummer) typically holds a pair o ...

, other musical instruments, or any items which made unusual loud noises that attracted the attention of the surrounding population. Whistles were used by police in the 19th century.

Steam whistle A steam whistle is a device used to produce sound in the form of a whistle using live steam, which creates, projects, and amplifies its sound by acting as a vibrating system (compare to train horn). Operation The whistle consists of the fo ...

s have been used on locomotives, ships, and in factories as alarm devices. With the advent of electricity, a variety of other alerting devices have been invented, such as

buzzer A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or piezoelectric (''piezo'' for short). Typical uses of buzzers and beepers include alarm devices, timers, train and confirmation of user input such as a ...

klaxon A horn is a sound-making device that can be equipped to motor vehicles, buses, bicycles, trains, trams (otherwise known as streetcars in North America), and other types of vehicles. The sound made usually resembles a "honk" (older vehicles) or a ...

sirens Siren or sirens may refer to: Common meanings * Siren (alarm), a loud acoustic alarm used to alert people to emergencies * Siren (mythology), an enchanting but dangerous monster in Greek mythology Places * Siren (town), Wisconsin * Siren, Wisco ...

horns Horns or The Horns may refer to: * Plural of Horn (instrument), a group of musical instruments all with a horn-shaped bells * The Horns (Colorado), a summit on Cheyenne Mountain * ''Horns'' (novel), a dark fantasy novel written in 2010 by Joe Hill ...

, flashing and coloured lights, and other all-purpose alarms. Alarm devices can be fitted to buildings as well as vehicles. Many buildings are fitted with

fire alarms A fire alarm system warns people when smoke, fire, carbon monoxide or other fire-related or general notification emergency, emergencies are detected. These alarms may be activated automatically from smoke detectors and heat detectors or may also ...

, ranging from a self-contained domestic

smoke detector A smoke detector is a device that senses smoke, typically as an indicator of fire. Smoke detectors are usually housed in plastic enclosures, typically shaped like a disk about in diameter and thick, but shape and size vary. Smoke can be detecte ...

to a sophisticated alarm system that can operate building fire fighting systems automatically to extinguish fires with water or inert gases. Many industries have developed standards for alarm devices, and the colours red, blue and amber are generally recognized as alarm device-related colours, with flashing lights often indicating urgent conditions.

Responses to an alarm

Human reactions to an alarm will often depend on upbringing, psychological training, or the behavior of others in the environment. Consequently, the ability to test an alarm and hold regular drills to practice an appropriate response may be provided as part of an alarm system. Alarm devices that are intended to cause the evacuation of an occupied building, such as fire alarms, may be deliberately designed to make remaining in the space difficult or even painful in order to encourage occupants to leave. Some alarms may startle and cause a

fight-or-flight response The fight-or-flight or the fight-flight-or-freeze response (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first des ...

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

s; a person under this mindset will panic and either flee the perceived danger or attempt to eliminate it, often ignoring rational thought in either case. A person in such a state can be characterized as "alarmed".

False alarms

With any kind of alarm, you must balance between the danger of false alarms (called "false positives") — the signal going off in the absence of a problem — or an alarm failing to signal an actual problem (called a "false negative"). False alarms can waste resources expensively and can even be dangerous. For example, false alarms of a fire can waste

firefighter A firefighter is a first responder and rescuer extensively trained in firefighting, primarily to extinguish hazardous fires that threaten life, property, and the environment as well as to rescue people and in some cases or jurisdictions also ...

manpower, making them unavailable for a real fire, and risk injury to firefighters and others as the fire engines race to the alleged fire's location. In addition, false alarms may acclimatise people to ignore alarm signals, and thus possibly to ignore an actual emergency:

Aesop Aesop ( or ; , ; c. 620–564 BCE) 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 cre ...

fable Fable is a literary genre: a succinct fictional story, in prose or verse, that features animals, legendary creatures, plants, inanimate objects, or forces of nature that are anthropomorphized, and that illustrates or leads to a particular mo ...

of ''

The Boy Who Cried Wolf The Boy Who Cried Wolf is one of Aesop's Fables, numbered 210 in the Perry Index. From it is derived the English idiom "to cry wolf", defined as "to give a false alarm" in e''Brewer's Dictionary of Phrase and Fable'' and glossed by the ''Oxford E ...

'' exemplifies this problem. A false alarm is one of the most significant issues with conventional alarm systems. They can be triggered for several reasons, such as the movement of pets, typing in the wrong security codes, or loud sounds from windows or doors. In the case of fire alarms, aerosol sprays, smoking, or burning food can all lead to a false alarm. Many avoid the risk of false alarms by ensuring their alarms are secured in an appropriate location, such as placing a smoke detector or fire alarm away from the kitchen where smoke from burned food or large quantities of steam which may trigger a false alarm are common occurrences. In the case of a security alarm, an additional monitoring station which assesses whether there is a legitimate need for help can reduce false alarms.

Devices

There are many kinds of alarm devices. The most common types include: * an alarm clock that sounds an alarm at a pre-set time, often used to wake a person up or remind them of an event. * a fire alarm which is used to give occupants of a building early warning of a potential fire and give them time to evacuate. * warning devices on a vehicle that sound when it is moving in an unexpected direction, such as reversing, * a siren, often accompanied by flashing coloured lights, on emergency vehicles responding to an emergency Alarm devices, by category, include: *

burglar alarm A security alarm is a system designed to detect intrusion, such as unauthorized entry, into a building or other areas such as a home or school. Security alarms used in residential, commercial, industrial, and military properties protect against ...

s, designed to warn of burglaries. This is often a silent alarm; law enforcement or guards are warned without alerting the

burglar Burglary, also called breaking and entering and sometimes housebreaking, is the act of entering a building or other areas without permission, with the intention of committing a criminal offence. Usually that offence is theft, robbery or murd ...

, which increases the chances of stopping the theft while in progress. *

alarm clock An alarm clock (or sometimes just an alarm) is a clock that is designed to alert an individual or group of individuals at a specified time. The primary function of these clocks is to awaken people from their night's sleep or short naps; they ar ...

s can beep, buzz or ring at a set time to wake a person up or for other reminders *

distributed control system A distributed control system (DCS) is a computerised control system for a process or plant usually with many control loops, in which autonomous controllers are distributed throughout the system, but there is no central operator supervisory contro ...

s (DCS), found in

nuclear power plants A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces elec ...

refineries A refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value. Types of refineries Different types of refineries ar ...

and chemical facilities, also generate alarms to direct the operator's attention to an important event that they need to address. * alarms in an operation and maintenance (O&M) monitoring system, which alerts an operator to a malfunction of a particular part of the system under monitoring. ** first-out alarm * safety alarms, which go off if a dangerous condition occurs. Common public safety alarms include: **

civil defense siren A civil defense siren, also known as an air-raid siren or tornado siren, is a siren used to provide an emergency population warning to the general population of approaching danger. It is sometimes sounded again to indicate the danger has pas ...

, also known as ''tornado sirens'' or ''air raid sirens'' **

fire alarm system A fire alarm system warns people when smoke, fire, carbon monoxide or other fire-related or general notification emergency, emergencies are detected. These alarms may be activated automatically from smoke detectors and heat detectors or may also ...

s ***

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. ...

*** "

Multiple-alarm fire One-alarm fires, two-alarm fires, three-alarm fires, etc., are categories classifying the seriousness of fires, commonly used in the United States and in Canada, particularly indicating the level of response by local authorities. The term multip ...

", a locally specific measure of the severity of a fire and the fire-department reaction required. ***

car alarm A car alarm is an electronic device installed in a vehicle in an attempt to discourage theft of the vehicle itself, its contents, or both. Car alarms work by emitting high-volume sound (often a vehicle-mounted siren, klaxon, pre-recorded verbal ...

s **

autodialer alarm An automatic dialer (also spelled auto dialer, auto-dialer, and autodialer) is an electronic device or software that automatically dials telephone numbers. Once the call has been answered, the autodialer either plays a recorded message or connec ...

, also known as ''community alarm'' ** personal alarm ** Video alarm verification systems provides instant notifications upon the detection of a possible threat verified through a video feed. ** tocsin – a historical alarm mechanism

References