Alarm clock
Overview
 
An alarm clock is a clock
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

 that is designed to make a loud sound at a specific time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

. The primary use of these clocks is to awake
Awake
Wakefulness is a daily recurring brain state and state of consciousness in which an individual is conscious and engages in a coherent cognitive and behavior responses to the external world such as communication, ambulation, nutritional ingestion and procreation...

n people from their night's sleep
Sleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...

 or short nap
Nap
A nap is a short period of sleep.Nap may also refer to:-Politics:* National Action Party , a political movement* National Action Plan on the Elimination of Child Labour...

s; they are sometimes used for other reminders as well. To stop the sound, a button or handle on the clock is pressed; but most clocks automatically stop the alarm sound if left unattended long enough. A classic analog alarm clock has an extra hand or inset dial that is used to specify the time at which to activate the alarm.

Traditional mechanical alarm clocks have one or two bell
Bell (instrument)
A bell is a simple sound-making device. The bell is a percussion instrument and an idiophone. Its form is usually a hollow, cup-shaped object, which resonates upon being struck...

s that ring by means of a mainspring
Mainspring
A mainspring is a spiral torsion spring of metal ribbon that is the power source in mechanical watches and some clocks. Winding the timepiece, by turning a knob or key, stores energy in the mainspring by twisting the spiral tighter. The force of the mainspring then turns the clock's wheels as it...

 that drives a gear that propels a hammer back and forth between the two bells or between the interior sides of a single bell.
Discussions
Encyclopedia
An alarm clock is a clock
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

 that is designed to make a loud sound at a specific time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

. The primary use of these clocks is to awake
Awake
Wakefulness is a daily recurring brain state and state of consciousness in which an individual is conscious and engages in a coherent cognitive and behavior responses to the external world such as communication, ambulation, nutritional ingestion and procreation...

n people from their night's sleep
Sleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...

 or short nap
Nap
A nap is a short period of sleep.Nap may also refer to:-Politics:* National Action Party , a political movement* National Action Plan on the Elimination of Child Labour...

s; they are sometimes used for other reminders as well. To stop the sound, a button or handle on the clock is pressed; but most clocks automatically stop the alarm sound if left unattended long enough. A classic analog alarm clock has an extra hand or inset dial that is used to specify the time at which to activate the alarm.

Traditional mechanical alarm clocks have one or two bell
Bell (instrument)
A bell is a simple sound-making device. The bell is a percussion instrument and an idiophone. Its form is usually a hollow, cup-shaped object, which resonates upon being struck...

s that ring by means of a mainspring
Mainspring
A mainspring is a spiral torsion spring of metal ribbon that is the power source in mechanical watches and some clocks. Winding the timepiece, by turning a knob or key, stores energy in the mainspring by twisting the spiral tighter. The force of the mainspring then turns the clock's wheels as it...

 that drives a gear that propels a hammer back and forth between the two bells or between the interior sides of a single bell. In some models, the back encasement of the clock itself acts as the bell. In an electric bell-style alarm clock, the bell is rung by an electromagnetic
Electromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...

 circuit
Electronic circuit
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...

 and armature
Armature (electrical engineering)
In electrical engineering, an armature generally refers to one of the two principal electrical components of an electromechanical machine–generally in a motor or generator, but it may also mean the pole piece of a permanent magnet or electromagnet, or the moving iron part of a solenoid or relay....

 that turns the circuit on and off repeatedly.

Digital alarm clocks can make other noises. Simple battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

-powered alarm clocks make a loud buzzing or beeping sound to wake a sleeper, while novelty alarm clocks can speak, laugh, sing, or play sounds from nature.

Some alarm clocks have radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

s that can be set to start playing at specified times, and are known as clock radios. A progressive alarm clock, still new in the market, can have different alarms for different times (see Next-Generation Alarms). Most modern televisions and cell phones have alarm clock functions to turn on or make sounds at specified times.

History

The ancient Greek
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

 philosopher Plato
Plato
Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...

 (428–348 BC) was said to possess a large water clock
Water clock
A water clock or clepsydra is any timepiece in which time is measured by the regulated flow of liquid into or out from a vessel where the amount is then measured.Water clocks, along with sundials, are likely to be the oldest time-measuring instruments, with the only exceptions...

 with an unspecified alarm signal similar to the sound of a water organ
Water organ
The water organ or hydraulic organ is a type of pipe organ blown by air, where the power source pushing the air is derived by water from a natural source or by a manual pump...

; he used it at night, possibly for signalling the beginning of his lectures at dawn (Athenaeus
Athenaeus
Athenaeus , of Naucratis in Egypt, Greek rhetorician and grammarian, flourished about the end of the 2nd and beginning of the 3rd century AD...

 4.174c). The Hellenistic engineer and inventor Ctesibius
Ctesibius
Ctesibius or Ktesibios or Tesibius was a Greek inventor and mathematician in Alexandria, Ptolemaic Egypt. He wrote the first treatises on the science of compressed air and its uses in pumps...

 (fl.
Floruit
Floruit , abbreviated fl. , is a Latin verb meaning "flourished", denoting the period of time during which something was active...

 285–222 BC) fitted his clepsydra
Clepsydra
Clepsydra may refer to:*Clepsydra , the Greek word for water clock. Also, in ancient Greece, a device for drawing liquids from vats too large to pour, which utilized the principles of air pressure to transport the liquid from one container to another.* Clepsydra Geyser in the Lower Geyser Basin of...

s with dial and pointer for indicating the time, and added elaborate "alarm systems, which could be made to drop pebbles on a gong, or blow trumpets (by forcing bell-jars down into water and taking the compressed air through a beating reed) at pre-set times" (Vitruv 11.11).

The late Roman
Late Antiquity
Late Antiquity is a periodization used by historians to describe the time of transition from Classical Antiquity to the Middle Ages, in both mainland Europe and the Mediterranean world. Precise boundaries for the period are a matter of debate, but noted historian of the period Peter Brown proposed...

 senator Cassiodorus
Cassiodorus
Flavius Magnus Aurelius Cassiodorus Senator , commonly known as Cassiodorus, was a Roman statesman and writer, serving in the administration of Theodoric the Great, king of the Ostrogoths. Senator was part of his surname, not his rank.- Life :Cassiodorus was born at Scylletium, near Catanzaro in...

 (c. 485–585) advocated in his rulebook for monastic life the water clock as a useful alarm for the 'soldiers of Christ
Christ
Christ is the English term for the Greek meaning "the anointed one". It is a translation of the Hebrew , usually transliterated into English as Messiah or Mashiach...

' (Cassiod. Inst. 30.4 f.). The Christian rhetorician Procopius
Procopius of Gaza
Procopius of Gaza was a Christian sophist and rhetorician, one of the most important representatives of the famous school of his native place...

 described in detail prior to 529 a complex public striking clock
Striking clock
A striking clock is a clock that sounds the hours audibly on a bell or gong. In 12 hour striking, used most commonly in striking clocks today, the clock strikes once at 1 AM, twice at 2 AM, continuing in this way up to twelve times at 12 noon, then starts over, striking once at 1 PM, twice at 2...

 in his home town Gaza
Gaza
Gaza , also referred to as Gaza City, is a Palestinian city in the Gaza Strip, with a population of about 450,000, making it the largest city in the Palestinian territories.Inhabited since at least the 15th century BC,...

 which featured an hourly gong and figures moving mechanically day and night.

In China, a striking clock
Striking clock
A striking clock is a clock that sounds the hours audibly on a bell or gong. In 12 hour striking, used most commonly in striking clocks today, the clock strikes once at 1 AM, twice at 2 AM, continuing in this way up to twelve times at 12 noon, then starts over, striking once at 1 PM, twice at 2...

 was devised by the Buddhist monk and inventor Yi Xing
Yi Xing
Yi Xing , born Zhang Sui , was a Chinese astronomer, mathematician, mechanical engineer,and Buddhist monk of the Tang Dynasty...

 (683–727). The Chinese engineers Zhang Sixun
Zhang Sixun
Zhang Sixun was a Chinese astronomer and military engineer from Bazhong, Sichuan during the early Song Dynasty . He is credited with creating an armillary sphere for his astronomical clock tower that employed the use of liquid mercury...

 and Su Song
Su Song
Su Song was a renowned Chinese polymath who specialized himself as a statesman, astronomer, cartographer, horologist, pharmacologist, mineralogist, zoologist, botanist, mechanical and architectural engineer, poet, antiquarian, and ambassador of the Song Dynasty .Su Song was the engineer of a...

 integrated striking clock mechanisms in astronomical clocks in the 10th and 11th centuries, respectively. A striking clock outside of China was the water-powered clock tower near the Umayyad Mosque
Umayyad Mosque
The Umayyad Mosque, also known as the Great Mosque of Damascus or formerly the Basilica of Saint John the Baptist , is located in the old city of Damascus, is one of the largest and oldest mosques in the world...

 in Damascus
Damascus
Damascus , commonly known in Syria as Al Sham , and as the City of Jasmine , is the capital and the second largest city of Syria after Aleppo, both are part of the country's 14 governorates. In addition to being one of the oldest continuously inhabited cities in the world, Damascus is a major...

, Syria
Syria
Syria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....

, which struck once every hour. It was constructs by the Arab engineer al-Kaysarani in 1154. In 1235, an early monumental water-powered alarm clock that "announced the appointed hours of prayer
Salat times
Salat times refers to times when Muslims perform prayers . The term is primarily used for the five daily prayers plus the Friday prayer. According to Muslim beliefs, the salat times were taught by Allah through Gabriel to Muhammad....

 and the time both by day and by night" was completed in the entrance hall of the Mustansiriya Madrasah in Baghdad
Baghdad
Baghdad is the capital of Iraq, as well as the coterminous Baghdad Governorate. The population of Baghdad in 2011 is approximately 7,216,040...

.

From the 14th century, some clock towers in Western Europe
Western Europe
Western Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...

 were also capable of chiming at a fixed time everyday, the earliest of which was described by the Florentine
Florence
Florence is the capital city of the Italian region of Tuscany and of the province of Florence. It is the most populous city in Tuscany, with approximately 370,000 inhabitants, expanding to over 1.5 million in the metropolitan area....

 writer Dante Alighieri
Dante Alighieri
Durante degli Alighieri, mononymously referred to as Dante , was an Italian poet, prose writer, literary theorist, moral philosopher, and political thinker. He is best known for the monumental epic poem La commedia, later named La divina commedia ...

 in 1319. The most famous original striking clock tower still standing is possibly the one in St Mark's Clocktower
St Mark's Clocktower
The Clock Tower in Venice is an early renaissance building on the north side of the Piazza San Marco at the entrance to the Merceria. It comprises a tower, which contains the clock, and lower buildings on each side. It adjoins the eastern end of the Procuratie Vecchie...

 in St Mark's Square, Venice
Venice
Venice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...

. The St Mark's Clock
St Mark's Clock
For the building containing the clock see the article on the ClocktowerSt Mark's Clock is the clock housed in the Clocktower on the Piazza San Marco in Venice adjoining the Procuratie Vecchie...

 was assembled in 1493, by the famous clockmaker Gian Carlo Rainieri from Reggio Emilia
Reggio Emilia
Reggio Emilia is an affluent city in northern Italy, in the Emilia-Romagna region. It has about 170,000 inhabitants and is the main comune of the Province of Reggio Emilia....

, where his father Gian Paolo Rainieri had already constructed another famous device in 1481. In 1497, Simone Campanato moulded the great bell (h. 1,56 m., diameter m. 1,27), which was put on the top of the tower where it's alternatively beaten by the Due Mori (Two Moors
Moors
The description Moors has referred to several historic and modern populations of the Maghreb region who are predominately of Berber and Arab descent. They came to conquer and rule the Iberian Peninsula for nearly 800 years. At that time they were Muslim, although earlier the people had followed...

), two bronze statues (h. 2,60) handling a hammer.

User-settable mechanical alarm clocks date back at least to 15th-century Europe. These early alarm clocks had a ring of holes in the clock dial and were set by placing a pin in the appropriate hole.

Another mechanical alarm clock was created by Levi Hutchins, of New Hampshire
New Hampshire
New Hampshire is a state in the New England region of the northeastern United States of America. The state was named after the southern English county of Hampshire. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Atlantic Ocean to the east, and the Canadian...

 in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, in 1787. This device he made only for himself however, and it only rang at 4 AM, in order to wake him for his job. The French inventor Antoine Redier was the first to patent an adjustable mechanical alarm clock, in 1847.

Alarm clocks, like almost all other consumer goods in the United States of America, ceased production in the spring of 1942, as the factories which made them were converted over to war work during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, but they were one of the first consumer items to resume manufacture for civilian use, in November 1944. By that time, a critical shortage of alarm clocks had developed due to older clocks wearing out or breaking down. Workers were late for, or missed completely, their scheduled shifts in jobs critical to the war effort because "my alarm clock is broken". In a pooling arrangement overseen by the Office of Price Administration
Office of Price Administration
The Office of Price Administration was established within the Office for Emergency Management of the United States government by Executive Order 8875 on August 28, 1941. The functions of the OPA was originally to control money and rents after the outbreak of World War II.President Franklin D...

, several clock companies were allowed to start producing new clocks, some of which were continuations of pre-war designs, and some of which were new designs, thus becoming among the first "postwar" consumer goods to be made, before the war had even ended. The price of these "emergency" clocks was, however, still strictly regulated by the Office of Price Administration. The first radio alarm clock was invented by James F. Reynolds, in the 1940s and another design was also invented by Paul L Schroth Sr.

Modern digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...

 alarm clocks typically feature a radio alarm function and/or beeping or buzzing alarm, allowing a sleeper to awaken to music or news radio rather than harsh noise. Most also offer a "snooze button", a large button on the top that stops the alarm and sets it to ring again at a short time later, most commonly nine minutes. Some alarm clocks also have a "sleep" button, which turns the radio on for a set amount of time (usually around one hour). This is useful for people who like to fall asleep with the radio on.

Digital clock radios often use a battery backup to maintain the time in the event of a power outage. Without this feature, digital clocks will reset themselves incorrectly (usually to midnight) when power is restored, causing a failure to trigger the alarm. To solve this issue, some digital clock radios trigger the alarm at e.g. 00:01 after a reset to midnight, so that at least the user is able to correct the clock and alarm time. Some other radio clock
Radio clock
A radio clock or radio-controlled clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock...

s (not to be confused with clocks with AM/FM radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

s) have a feature which sets the time automatically using signals from atomic clock
Atomic clock
An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...

-synced time signal
Time signal
A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.-Audible and visible time signals:...

 radio station
Radio station
Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both...

s such as WWV, making the clock ready for use right out of the box.

Other alarm signals

The deaf and hard of hearing are often unable to perceive auditory alarms when asleep. They may use specialized alarms, including alarms with flashing lights instead of or in addition to noise. Alarms which can connect to vibrating devices (small ones inserted into pillows, or larger ones placed under bedposts to shake the bed) also exist.

Computer alarms

Alarm clock software programs have been developed for personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...

s. A computer acting as an alarm clock may allow a virtually unlimited number of alarm times (ie : Personal information manager
Personal information manager
A personal information manager is a type of application software that functions as a personal organizer. The acronym PIM is now, more commonly, used in reference to Personal information management as a field of study...

) and personalized tones. Online alarm clocks are also available.

Cell phone alarms

Many modern cell phones feature built-in alarms that do not require the phone to be powered on for the alarm to go off. Some of these cell phones feature the ability for the user to set the tone of the alarm, and in some cases music can be downloaded to the phone and then chosen to play for waking.

Next-generation alarms

Among annoyances caused by alarm clocks is sleep inertia
Sleep inertia
Sleep inertia is a physiological state characterised by a decline in motor dexterity and a subjective feeling of grogginess immediately following an abrupt awakening. The impaired alertness may interfere with the ability to perform mental or physical tasks...

, a feeling of grogginess that results from abrupt awakening. Progressive alarm clocks claim to solve this issue. They include sunrise alarm clocks, dawn simulators
Dawn simulation
Dawn simulation is a technique originally developed to help treat seasonal affective disorder, but can be used as a soundless alarm clock to wake up the body naturally...

 and progressive auditory alarm clocks.

Sleepers can become accustomed to the sound of their alarm clock if it has been used for a period of time, making it less effective. Because progressive alarm clocks have a complex waking procedure, they can deter this adaptation due to the body needing to adapt to more stimuli than just a simple sound alert.

Scientific studies on sleep having shown that sleep stage at awakening is an important factor in amplifying sleep inertia. Alarm clocks involving sleep stage monitoring appeared on the market in 2005. Using sensing technologies such as EEG
Electroencephalography
Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...

 electrodes or accelerometers, these alarm clocks are supposed to wake people only from light sleep.

See also

  • Delayed sleep phase syndrome
    Delayed sleep phase syndrome
    Delayed sleep-phase syndrome , also known as delayed sleep-phase disorder or delayed sleep-phase type , is a circadian rhythm sleep disorder, a chronic disorder of the timing of sleep, peak period of alertness, the core body temperature rhythm, hormonal and other daily rhythms, compared to the...

  • Digital clock
    Digital clock
    A digital clock is a type of clock that displays the time digitally, i.e. in cyphers, as opposed to an analog clock, where the time is displayed by hands. Digital clocks are often associated with electronic drives, but the "digital" description refers only to the display, not to the drive mechanism...

  • Light therapy
    Light therapy
    Light therapy or phototherapy consists of exposure to daylight or to specific wavelengths of light using lasers, light-emitting diodes, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, usually controlled with various devices...

  • Timer
    Timer
    A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Whereas a stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass.Timers can be mechanical, electromechanical,...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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