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Voice-activated Radio-dispatched Alarm
A voice-activated radio-dispatched alarm, or VARDA-alarm, is a type of burglar alarm that, when activated or "tripped", broadcasts the type of the alarm and the transmitter location over the local police radio frequency using a pre-recorded audio message. In 1968, the voice-activated radio dispatched alarm (VARDA), was invented. It is a portable device that, when activated, will broadcast a message to the dispatch channel, allowing officers to immediately respond to the scene for further investigation. Although the VARDA was originally designed for law enforcement applications such as repeat break-ins, domestic violence issues and metal/equipment theft, its concept has been adapted over time to address a variety of needs in the private sector. This type of alarm is installed for special monitoring at the location of recent burglaries. When the alarm is activated, it will set off a voice message directly over a radio frequency (generally a non-primary frequency), repeating the me ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Security 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 burglary (theft) or property damage, as well as personal protection against intruders. Security alerts in neighborhoods show a connection with diminished robbery. Car alarms likewise help protect vehicles and their contents. Prisons also use security systems for the control of inmates. Some alarm systems serve a single purpose of burglary protection; combination systems provide fire and intrusion protection. Intrusion-alarm systems are combined with closed-circuit television surveillance (CCTV) systems to record intruders' activities and interface to access control systems for electrically locked doors. There are many types of security systems. Homeowners typically have small, self-contained noisemakers. These devices can also be complicat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Broadcasting
Broadcasting is the distribution (business), distribution of sound, audio or video content to a dispersed audience via any electronic medium (communication), mass communications medium, but typically one using the electromagnetic spectrum (radio waves), in a :wikt:one-to-many, one-to-many model. Broadcasting began with AM radio, which came into popular use around 1920 with the spread of vacuum tube radio transmitters and radio receiver, receivers. Before this, all forms of electronic communication (early radio, telephone, and telegraph) were wikt:one-to-one, one-to-one, with the message intended for a single recipient. The term ''broadcasting'' evolved from its use as the agricultural method of sowing seeds in a field by casting them broadly about. It was later adopted for describing the widespread distribution of information by printed materials or by telegraph. Examples applying it to "one-to-many" radio transmissions of an individual station to multiple listeners appeared as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transmitter
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna (radio), antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the Antenna (radio), antenna. When excited by this alternating current, the antenna radiates radio waves. Transmitters are necessary component parts of all electronic devices that communicate by radio communication, radio, such as radio broadcasting, radio and television broadcasting stations, cell phones, walkie-talkies, Wireless LAN, wireless computer networks, Bluetooth enabled devices, garage door openers, two-way radios in aircraft, ships, spacecraft, radar sets and navigational beacons. The term ''transmitter'' is usually limited to equipment that generates radio waves for Communication engineering, communication purposes; or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heatin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Location (geography)
In geography, location or place are used to denote a region (point, line, or area) on Earth's surface or elsewhere. The term ''location'' generally implies a higher degree of certainty than ''place'', the latter often indicating an entity with an ambiguous boundary, relying more on human or social attributes of place identity and sense of place than on geometry. Types Locality A suburb, locality, human settlement, settlement, or populated place is likely to have a well-defined name but a boundary that is not well defined varies by context. London, for instance, has a legal boundary, but this is unlikely to completely match with general usage. An area within a town, such as Covent Garden in London, also almost always has some ambiguity as to its extent. In geography, location is considered to be more precise than "place". Relative location A relative location, or situation, is described as a displacement from another site. An example is "3 miles northwest of Seattle". Absolute lo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Police Radio
Police radio is a radio system used by police and other law enforcement agencies to communicate with one another. Police radio systems almost always use two-way radio systems to allow for communications between police officers and dispatchers. Most modern police radio systems are encrypted, and many jurisdictions have made listening to police radio frequencies as a private citizen illegal. History Before police radio systems were first implemented, police officers assigned to their beat could only communicate with police command using telephone booths, call boxes, police boxes, or physical meetings. Calling for help or signaling other officers could only be done by shouting, using a whistle, or hitting things to make sounds. This meant that properly calling for assistance, reporting an incident or arrest, being dispatched to handle a crime, or requesting police resources was only possible if the officer reached a telephone or call box. The first police radio systems were i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radio Frequency
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upper limit of audio frequencies and the lower limit of infrared frequencies; these are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves. Different sources specify different upper and lower bounds for the frequency range. Electric current Electric currents that oscillate at radio frequencies (RF currents) have special properties not shared by direct current or lower audio frequency alternating current, such as the 50 or 60 Hz current used in electrical power distribution. * Energy from RF currents in conductors can radiate into space as electromagnetic waves ( radio waves). This is the basis of radio technology. * RF current does not penetrate deeply into electrical c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Message
A message is a discrete unit of communication intended by the source for consumption by some recipient or group of recipients. A message may be delivered by various means, including courier, telegraphy, carrier pigeon and electronic bus. A message can be the content of a broadcast. An interactive exchange of messages forms a conversation. One example of a message is a press release, which may vary from a brief report or statement released by a public agency to commercial publicity material. History Roles in human communication In communication between humans, messages can be verbal or nonverbal: * A verbal message is an exchange of information using words. Examples include face-to-face communication, telephone calls, voicemails, email etc. * A nonverbal message is communicated through actions or behaviors rather than words, such as conscious or unconscious body language. In computer science There are two main senses of the word "message" in computing: messages be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amateur Radio Emergency Communications
In times of crisis and natural disasters, amateur radio is often used as a means of emergency communication when wireline, cell phones and other conventional means of communications fail. Unlike commercial systems, amateur radio is usually independent of terrestrial facilities that can fail. It is dispersed throughout a community without "choke points" such as cellular telephone sites that can be overloaded. Amateur radio operators are experienced in improvising antennas and power sources and most equipment today can be powered by an automobile battery. Annual " Field Days" are held in many countries to practice these emergency improvisational skills. Amateur radio operators can use hundreds of frequencies and can quickly establish networks tying disparate agencies together to enhance interoperability. Recent examples include the September 11 attacks on the World Trade Center in Manhattan in 2001, the 2003 North America blackout and Hurricane Katrina in September 2005, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Emergency Alert System
The Emergency Alert System (EAS) is a national warning system in the United States designed to allow authorized officials to broadcast emergency alerts and warning messages to the public via cable, satellite, or broadcast television, and both AM/ FM and satellite radio. The EAS became operational on January 1, 1997, after being approved by the Federal Communications Commission (FCC) in November 1994, replacing the Emergency Broadcast System (EBS). Its main improvement over the EBS, and perhaps its most distinctive feature, is its application of a digitally encoded audio signal known as Specific Area Message Encoding (SAME), which is responsible for the "screeching" or "chirping" sounds at the start and end of each message. This signal encodes locations an alert applies to, useful for specialized encoding and decoding equipment at broadcasting stations to automatically filter alert messages that do not apply to the area and to relay messages that do. Like the EBS, the system ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Message In A Bottle
A message in a bottle (abbrev. MIB) is a form of communication in which a message is sealed in a container (typically a bottle) and released into a conveyance medium (typically a body of water). Messages in bottles have been used to send distress messages, in crowdsourced scientific studies of ocean currents, as memorial tributes, to send deceased loved ones' ashes on a final journey, to convey expedition reports, and to carry letters or reports from those believing themselves to be doomed. Invitations to prospective pen pals and letters to actual or imagined love interests have also been sent as messages in bottles. The lore surrounding messages in bottles has often been of a romantic or poetic nature. Use of the term "message in a bottle" has expanded to include metaphorical uses or uses beyond its traditional meaning as bottled messages released into oceans. The term has been applied to plaques on craft launched into outer space, interstellar radio messages, stationary time ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Smoke Signals
The smoke signal is one of the oldest forms of long-distance communication. It is a form of visual communication used over a long distance. In general smoke signals are used to transmit news, signal danger, or to gather people to a common area. History and usage In ancient China, soldiers along the Great Wall sent smoke signals on its beacon towers to warn one another of enemy invasion. The colour of the smoke communicated the size of the invading party. By placing the beacon towers at regular intervals, and situating a soldier in each tower, messages could be transmitted over the entire 7,300 kilometres of the Wall. Smoke signals also warned the inner castles of the invasion, allowing them to coordinate a defense and garrison supporting troops. In ancient Sri Lanka, soldiers stationed on the mountain peaks would alert each other of impending enemy attack (from English people, Dutch people or Portuguese people) by signaling from peak to peak. In this way, they were able to t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alarms
An alarm device is a mechanism that gives an audible, visual or other kind of alarm signal to alert someone to a problem or condition that requires urgent attention. Alphabetical musical instruments Etymology The word ''alarm'' comes from the Old French ''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 ''all'armi'' and appears 89 times in Shakespeare's first folio. 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 bells, drums, other musical instruments, or any items which made unusual loud noises that attracted the attention o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
