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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. [1] In 1968, the voice-activated radio dispatched alarm (VARDA), was invented.
A security alarm is a system designed to detect intrusions, such as unauthorized entry, into a building or other areas, such as a home or school. Security alarms protect against burglary or property damage, as well as against intruders. Examples include personal systems, neighborhood security alerts, car alarms, and prison alarms.
When an electric current is applied, it produces a repetitive buzzing, clanging or ringing sound. Electromechanical bells have been widely used at railroad crossings, in telephones, fire and burglar alarms, as school bells, doorbells, and alarms in industrial areas, since the late 1800s, but they are now being widely replaced with electronic ...
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,
The Mosquito or Mosquito alarm is a machine used to deter loitering by emitting sound at high frequency. In some versions, it is intentionally tuned to be heard primarily by younger people. Nicknamed "Mosquito" for the buzzing sound it plays, the device is marketed as a safety and security tool for preventing youths from congregating in ...
Early devices were based on an electromechanical system identical to an electric bell without the metal gong. Similarly, a relay may be connected to interrupt its own actuating current, causing the contacts to buzz (the contacts buzz at line frequency if powered by alternating current) Often these units were anchored to a wall or ceiling to use it as a sounding board.
The sound emitted can also have the effect of distracting, disorienting, or surprising the assailant. The volume varies from model to model, with some models having 130 decibels . Some personal alarms are also outfitted with an LED light for normal lighting purposes or to help deter an assailant.
There are 8,200 alarm sirens for civil protection throughout Switzerland. They are tested once a year, on the first Wednesday in February. [1] Sound sample ⓘ An 1860s-era siren. [2] A siren is a loud noise-making device. There are two general types: mechanical and electronic.
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