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A smoke detector is a device that senses smoke, typically as an indicator of fire. Commercial security devices issue a signal to a fire alarm control panel as part of a fire alarm system, while household detectors, known as smoke alarms, generally issue a local audible or visual alarm from the detector itself. Smoke detectors are typically housed in a disk-shaped plastic enclosure about in diameter and thick, but the shape can vary by manufacturer or product line. Most smoke detectors work either by optical detection (photoelectric) or by physical process (ionization), while others use both detection methods to increase sensitivity to smoke. Sensitive alarms can be used to detect, and thus deter, smoking in areas where it is banned. Smoke detectors in large commercial, industrial, and residential buildings are usually powered by a central fire alarm system, which is powered by the building power with a battery backup. However, in many single-family detached and smaller multiple family housings, a smoke alarm is often powered only by a single disposable battery. it is estimated that smoke detectors are installed in 93 percent of US homes and 85 percent of UK homes. Roughly 30 percent of these alarms are estimated to not work, due to aging, removal of batteries, or failure of owners to replace dead batteries. In the United States, the National Fire Protection Association estimates that nearly two-thirds of deaths from home fires occur in properties without working smoke detectors. == History == The first automatic electric fire alarm was patented in 1890 by Francis Robbins Upton, an associate of Thomas Edison. George Andrew Darby patented the first European electrical heat detector in 1902 in Birmingham, England. In the late 1930s, Swiss physicist Walter Jaeger tried to invent a sensor for poison gas. He expected that gas entering the sensor would bind to ionized air molecules and thereby alter an electric current in a circuit in the instrument.〔 His device failed: small concentrations of gas had no effect on the sensor's conductivity.〔 Frustrated, Jaeger lit a cigarette and was soon surprised to notice that a meter on the instrument had registered a drop in current. Smoke particles from his cigarette had apparently done what poison gas could not.〔 Jaeger's experiment was one of the advances that paved the way for the modern smoke detector.〔 In 1939 Swiss physicist Dr. Ernst Meili devised an ionisation chamber device capable of detecting combustible gases in mines. He also invented a cold-cathode tube that could amplify the small electronic signal generated by the detection mechanism to a strength sufficient enough to activate an alarm.〔 Ionisation smoke detectors were first placed on the market in the United States in 1951 and were used only in major commercial and industrial facilities in the next several years due to their high expense and large size.〔 In 1955, simple home "fire detectors" for homes were invented. They detected high temperatures as the fire cue.〔 The United States Atomic Energy Commission (USAEC) granted the first license to distribute smoke detectors using radioactive material in 1963.〔 The first truly affordable home smoke detector was invented by Duane D. Pearsall in 1965, featuring an individual battery powered unit that could be easily installed and replaced. These first units, dubbed "SmokeGard 700," were made from strong fire resistant steel and shaped much like bee hives. The company began mass-producing these units in 1975.〔 Studies in the 1960s determined that smoke detectors respond to fires much faster than heat detectors. The first single-station smoke detector was invented in 1970 and made public the next year.〔 It was an ionisation detector powered by a single 9-volt battery.〔 They cost about $125 and sold at a rate of a few hundred thousand per year.〔 Several technological developments occurred between 1971 and 1976, including the replacement of cold-cathode tubes with solid-state circuitry, which greatly reduced the detectors' sizes and made it possible to monitor both the decrease in voltage and the build-up of internal resistance in the battery.〔 The previous alarm horns, which required specialty batteries were replaced with horns that were more energy-efficient, enabling the use of commonly available sizes of batteries.〔 These detectors could also function with smaller amounts of radioactive source material, and the sensing chamber and smoke detector enclosure were redesigned for more effective operation.〔 The rechargeable batteries were also replaced with a pair of AA batteries along with a plastic shell encasing the detector. The 10-year-lithium-battery-powered smoke alarm was invented in 1995.〔 The optical smoke detector was invented Donald Steele and Robert Enmark of Electro Signal and patented in 1972. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「smoke detector」の詳細全文を読む スポンサード リンク
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