A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More modern examples include a variety of radio beacons that can be read on radio direction finders in all weather, and radar transponders that appear on radar displays.
Beacons can also be combined with semaphoric or other indicators to provide important information, such as the status of an airport, by the colour and rotational pattern of its airport beacon, or of pending weather as indicated on a weather beacon mounted at the top of a tall building or similar site. When used in such fashion, beacons can be considered a form of optical telegraphy.
Beacons help guide navigators to their destinations. Types of navigational beacons include radar reflectors, radio beacons, sonic and visual signals. Visual beacons range from small, single-pile structures to large lighthouses or light stations and can be located on land or on water. Lighted beacons are called lights; unlighted beacons are called daybeacons . Aerodrome beacons are used to indicate locations of airports and helipads.
Handheld beacons are also employed in aircraft marshalling, and are used by the marshal to deliver instructions to the crew of aircraft as they move around an active airport, heliport or aircraft carrier.
Historically, beacons were fires lit at well-known locations on hills or high places, used either as lighthouses for navigation at sea, or for signalling over land that enemy troops were approaching, in order to alert defenses. As signals, beacons are an ancient form of optical telegraph and were part of a relay league.
Systems of this kind have existed for centuries over much of the world. The ancient Greeks called them phryctoriae , while beacons figure on several occasions on the column of Trajan.
In ancient China, sentinels on and near the Great Wall of China used a sophisticated system of daytime smoke and nighttime flame to send signals along long chains of beacon towers. 
Legend has it that Zhōu Yōu Wáng, king of the Western Zhou dynasty, played a trick multiple times in order to amuse his often melancholy concubine, ordering beacon towers lit to fool his Marquess and soldiers. But when enemies, led by Marquess of Shen really arrived at the wall, although the towers were lit, no defenders came, leading to Yōu's death and the collapse of the Western Zhou dynasty.   
Thucydides wrote that during the Peloponnesian War, the Peloponnesians who were in Corcyra were informed by night-time beacon signals of the approach of sixty Athenian vessels from Lefkada. 
In the 10th century, during the Arab–Byzantine wars, the Byzantine Empire used a beacon system to transmit messages from the border with the Abbasid Caliphate, across Anatolia to the imperial palace in the Byzantine capital, Constantinople. It was devised by Leo the Mathematician for Emperor Theophilos, but either abolished or radically curtailed by Theophilos' son and successor, Michael III.  Beacons were later used in Greece as well, while the surviving parts of the beacon system in Anatolia seem to have been reactivated in the 12th century by Emperor Manuel I Komnenos. 
In Scandinavia many hill forts were part of beacon networks to warn against invading pillagers. In Finland, these beacons were called vainovalkeat, "persecution fires", or vartiotulet, "guard fires", and were used to warn Finn settlements of imminent raids by the Vikings.
In Wales, the Brecon Beacons were named for beacons used to warn of approaching English raiders. In England, the most famous examples are the beacons used in Elizabethan England to warn of the approaching Spanish Armada. Many hills in England were named Beacon Hill after such beacons. In England the authority to erect beacons originally lay with the King and later was delegated to the Lord High Admiral. The money due for the maintenance of beacons was called Beaconagium and was levied by the sheriff of each county.  In the Scottish borders country, a system of beacon fires was at one time established to warn of incursions by the English. Hume and Eggerstone castles and Soltra Edge were part of this network. 
In Spain, the border of Granada in the territory of the Crown of Castile had a complex beacon network to warn against Moorish raiders and military campaigns.  Due to the progressive advance of the borders throughout the process of the Reconquista, the entire Spanish geography is full of defensive lines of castles, towers and fortifications, visually connected to each other, which served as fortified beacons. Some examples are the Route of the Vinalopó castles or the distribution of the castles in Jaén.
Infrared strobes and other infrared beacons have increasingly been used in modern combat when operating at night as they can only be seen through night vision goggles. As a result, they are often used to mark friendly positions as a form of IFF to prevent friendly fire and improve coordination. Soldiers will typically affix them to their helmets or other gear so they are easily visible to others using night vision including other infantry, ground vehicles, and aerial platforms (drones, helicopters, planes, etc). 
Passive markers include IR patches, which reflect infrared light, and chemlights. The earliest such beacons were often IR chemlights taped to helmets.
As time went on, more sophisticated options began to emerge with electronically powered infrared strobes with specific mounting solutions for attaching to helmets or load bearing equipment. These strobes may have settings which allow constant on or strobes of IR light, hence the name. 
Advancements in near-peer technology, however, present risk since if friendly units can see the strobe with night vision so could enemies with night vision capabilities. As a result, some in the American military have stressed that efforts should be made to improve training regarding light discipline (IR and visible) and other means of reducing a unit's visible signature. 
Vehicular beacons are rotating or flashing lights affixed to the top of a vehicle to attract the attention of surrounding vehicles and pedestrians. Emergency vehicles such as fire engines, ambulances, police cars, tow trucks, construction vehicles, and snow-removal vehicles carry beacon lights.
The color of the lamps varies by jurisdiction; typical colors are blue and/or red for police, fire, and medical-emergency vehicles; amber for hazards (slow-moving vehicles, wide loads, tow trucks, security personnel, construction vehicles, etc.); green for volunteer firefighters or for medical personnel, and violet for funerary vehicles. Beacons may be constructed with halogen bulbs similar to those used in vehicle headlamps, xenon flashtubes, or LEDs.  Incandescent and xenon light sources require the vehicle's engine to continue running to ensure that the battery is not depleted when the lights are used for a prolonged period. The low power consumption of LEDs allows the vehicle's engine to remain turned off while the lights operate.
Beacons and bonfires are also used to mark occasions and celebrate events.
Beacons have also allegedly been abused by shipwreckers. An illicit fire at a wrong position would be used to direct a ship against shoals or beaches, so that its cargo could be looted after the ship sank or ran aground. There are, however, no historically substantiated occurrences of such intentional shipwrecking.
In wireless networks, a beacon is a type of frame which is sent by the access point (or WiFi router) to indicate that it is on.
Bluetooth based beacons periodically send out a data packet and this could be used by software to identify the beacon location. This is typically used by indoor navigation and positioning applications. 
Beaconing is the process that allows a network to self-repair network problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.
In Aeschylus' tragedy Agamemnon ,  a chain of eight beacons staffed by so-called lampadóphoroi inform Clytemnestra in Argos, within a single night's time, that Troy has just fallen under her husband king Agamemnon's control, after a famous ten years siege.
In J. R. R. Tolkien's high fantasy novel, The Lord of the Rings , a series of beacons alerts the entire realm of Gondor when the kingdom is under attack. These beacon posts were staffed by messengers who would carry word of their lighting to either Rohan or Belfalas.  In Peter Jackson's film adaptation of the novel, the beacons serve as a connection between the two realms of Rohan and Gondor, alerting one another directly when they require military aid, as opposed to relying on messengers as in the novel.
The Beacon was an influential Caribbean magazine published in Trinidad in the 1930s. New Beacon Books was the first Caribbean publishing house in England, founded in London in 1966, was named after the Beacon journal. 
Beacons are sometimes used in retail to send digital coupons or invitations to customers passing by.  
This section needs expansion. You can help by adding to it. (June 2008)
An infrared beacon (IR beacon) transmits a modulated light beam in the infrared spectrum, which can be identified easily and positively. A line of sight clear of obstacles between the transmitter and the receiver is essential. IR beacons have a number of applications in robotics and in Combat Identification (CID).
Infrared beacons are the key infrastructure for the Universal Traffic Management System (UTMS) in Japan. They perform two-way communication with travelling vehicles based on highly directional infrared communication technology and have a vehicle detecting capability to provide more accurate traffic information. 
This section needs expansion. You can help by adding to it. (September 2012)
A sonar beacon is an underwater device which transmits sonic or ultrasonic signals for the purpose of providing bearing information. The most common type is that of a rugged watertight sonar transmitter attached to a submarine and capable of operating independently of the electrical system of the boat. It can be used in cases of emergencies to guide salvage vessels to the location of a disabled submarine. 
A lighthouse is a tower, building, or other type of physical structure designed to emit light from a system of lamps and lenses and to serve as a beacon for navigational aid, for maritime pilots at sea or on inland waterways.
Optical communication, also known as optical telecommunication, is communication at a distance using light to carry information. It can be performed visually or by using electronic devices. The earliest basic forms of optical communication date back several millennia, while the earliest electrical device created to do so was the photophone, invented in 1880.
A strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of light. It is one of a number of devices that can be used as a stroboscope. The word originated from the Ancient Greek στρόβος (stróbos), meaning "act of whirling".
A distress signal, also known as a distress call, is an internationally recognized means for obtaining help. Distress signals are communicated by transmitting radio signals, displaying a visually observable item or illumination, or making a sound audible from a distance.
A navigation light, also known as a running or position light, is a source of illumination on a watercraft, aircraft or spacecraft, meant to give information on the craft's position, heading, or status. Some navigation lights are colour-coded red and green to aid traffic control by identifying the craft's orientation. Their placement is mandated by international conventions or civil authorities such as the International Maritime Organization (IMO).
Marblehead Lighthouse in Marblehead, Ohio, United States, is the oldest lighthouse in continuous operation on the American side of the Great Lakes. It has guided sailors safely along the rocky shores of Marblehead Peninsula since 1822, and is an active aid to navigation.
North Foreland is a chalk headland on the Kent coast of southeast England, specifically in Broadstairs.
A motor vehicle has lighting and signaling devices mounted to or integrated into its front, rear, sides, and, in some cases, top. The devices illuminate the road ahead for the driver and increase the vehicle's visibility, allowing other drivers and pedestrians to see its presence, position, size, direction of travel, and its driver's intentions.
Emergency vehicle lighting, also known as simply emergency lighting or emergency lights, is a type of vehicle lighting used to visually announce a vehicle's presence to other road users. A sub-type of emergency vehicle equipment, emergency vehicle lighting is generally used by emergency vehicles and other authorized vehicles in a variety of colors.
The Baily Lighthouse is a lighthouse on the southeastern part of Howth Head in County Dublin, Ireland. It is maintained by the Commissioners of Irish Lights.
Emergency vehicle equipment is any equipment fitted to, or carried by, an emergency vehicle, other than the equipment that a standard non-emergency vehicle is fitted with.
The Lizard Lighthouse is a lighthouse at Lizard Point, Cornwall, England, built to guide vessels passing through the English Channel. It was often the welcoming beacon to persons returning to England, where on a clear night, the reflected light could be seen 100 mi (160 km) away.
The New Presque Isle Light was built in 1870, at Presque Isle, Michigan, east of Grand Lake, and sits on the namesake peninsula. It is one of 149 lighthouses in Michigan, more than any other state. Because of changing shoreline particularly, or alternatively deterioration of the original building, it is not uncommon for a replacement lighthouse to be placed in the vicinity of an earlier light, in this case, the Old Presque Isle Light.
Traffic signal preemption is a system that allows an operator to override the normal operation of traffic lights. The most common use of these systems manipulates traffic signals in the path of an emergency vehicle, halting conflicting traffic and allowing the emergency vehicle right-of-way, thereby reducing response times and enhance traffic safety. Signal preemption can also be used on tram, light-rail and bus rapid transit systems, to allow public transportation priority access through intersections, and by railroad systems at crossings to prevent collisions.
In traffic engineering, there are regional and national variations in traffic light operation. This may be in the standard traffic light sequence or by the use of special signals.
The Hook Lighthouse is a building situated on Hook Head at the tip of the Hook Peninsula in County Wexford, in Ireland. It is one of the oldest lighthouses in the world and the second oldest operating lighthouse in the world, after the Tower of Hercules in Spain. It is operated by the Commissioners of Irish Lights, the Irish lighthouse authority, and marks the eastern entrance to Waterford Harbour. The current structure has stood for over 800 years.
Aviation obstruction lighting is used to enhance the visibility of structures or fixed obstacles which may conflict with the safe navigation of aircraft. Obstruction lighting is commonly installed on towers, buildings, and even fences located in areas where aircraft may be operating at low altitudes. In certain areas, some aviation regulators mandate the installation, operation, color, and/or status notification of obstruction lighting. For maximum visibility and collision-avoidance, these lighting systems commonly employ one or more high-intensity strobe or LED devices which can be seen by pilots from many miles away from the obstruction.
Rotating beacon may refer to:
Belgian railway signalling is the signalling in effect on the Belgian rail network currently operated by Infrabel.
Semaphore is the use of an apparatus to create a visual signal transmitted over distance. A semaphore can be performed with devices including: fire, lights, flags, sunlight, and moving arms. Semaphores can be used for telegraphy when arranged in visually connected networks, or for traffic signalling such as in railway systems, or traffic lights in cities.