fire alarm
1. a signal that warns that a fire has started.
2. a bell, buzzer, siren, horn, etc., that provides such a signal.
[1840-50, Amer.]

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      means of warning in case of fire. Originally, watchmen provided the only fire-alarm system, but, with the advent of electric power, boxes wired to fire departments provided a warning system from city streets and such institutional buildings as schools. While some of the latter remain in use, most modern fire-alarm systems are automatic, consisting of thermostat-activated devices that at a certain temperature either sound an alarm or report to a central office, such as a municipal fire station. Some alarms are set to go off whenever the thermostat shows a rapid temperature rise. The thermostat is usually placed at or near the ceiling, where it will be most immediately affected by increase in temperature. Another type of alarm is actuated by a photoelectric cell; (photoelectric cell) when smoke darkens the room slightly, the alarm is activated. One highly sensitive device contains a small amount of radioactive material that ionizes the air in a chamber. With this device a continuously applied voltage causes a small electrical current to flow through the ionized air, and when products of combustion enter, they reduce the current flow and activate the alarm.

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Universalium. 2010.

Look at other dictionaries:

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  • fire alarm — fire a.larm n a piece of equipment that makes a loud noise to warn people of a fire in a building ▪ We were in the middle of an exam when the fire alarm went off . ▪ Someone set off the fire alarm …   Dictionary of contemporary English

  • fire alarm — [n] smoke detector danger signal, emergency alarm, fire bell, heat sensor, siren, smoke alarm; concepts 269,463 …   New thesaurus

  • fire alarm — fire alarms N COUNT A fire alarm is a device that makes a noise, for example with a bell, to warn people when there is a fire …   English dictionary

  • fire alarm — ► NOUN ▪ a device making a loud noise that gives warning of a fire …   English terms dictionary

  • fire alarm — n. 1. a signal to announce the outbreak of a fire, the activation of a smoke detector, etc. 2. a bell, siren, whistle, flashing light, etc. to give this signal …   English World dictionary

  • fire alarm — noun 1. a shout or bell to warn that fire has broken out • Hypernyms: ↑alarm, ↑alert, ↑warning signal, ↑alarum 2. an alarm that is tripped off by fire or smoke • Syn: ↑smoke alarm • Hyperny …   Useful english dictionary

  • fire alarm — n. 1) to set a fire alarm 2) to activate, set off, trigger a fire alarm 3) a fire alarm goes off, rings * * * [ faɪ(ə)rəˌlɑːm] rings set off trigger a fire alarm a fire alarm goes off to activate to set a fire alarm …   Combinatory dictionary

  • fire alarm — noun VERB + FIRE ALARM ▪ set off ▪ It was thought that the fire alarm had been set off as a prank. ▪ install ▪ Fire alarms have been installed in the building. FIRE ALARM + VERB …   Collocations dictionary

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