Installing at least one smoke detector in your house Is estimated to halve the chances of a fatal fire, which means that thousands of lives have been saved worldwide since home devices were introduced in the late 1960s.
The forerunner of the modern detector was invented by the British electrical engineer George Darby in 1902. His device, which detected heat rather than smoke, consisted of two electrical plates with a wedge of butter between them. As the room temperature rose, the butter melted, causing the two plates to fall onto each other triggering the alarm, and presumably dripping butter everywhere.
The most common smoke detectors now use an ionization chamber, a device developed by the Swiss physicist Ernst Meili in 1939 to detect poisonous gases in mines, although not specifically smoke. In the ionization chamber, a radioactive material produces ions (electrically charged atoms). In the presence of smoke, the flow of these ions between two electrodes is disturbed, triggering the alarm.
Although ionization chamber smoke detectors were available in the 1950s, they were expensive and used only in factories and other large buildings. The American Duane Pearsall (b. 1922) is credited with the first practical home smoke alarm in 1967, achieved by adding a battery to power a more compact ionization chamber. Two other Americans, Kenneth House and Randolph Smith, may have been the first to patent the battery-powered smoke detector in 1969. Even the National Aeronautics and Space Administration (NASA) is thought to have created the smoke detector as a spin- off from the space program. In fact NASA developed a type of detector for the Skylab project but did not invent the detector itself.
