Smoke detectors are one of those amazing inventions that, because of mass production, cost really cheap (below $10 in some stores in the US). But despite their minuscule cost, smoke detectors save thousands of lives each year. .
A smoke detector is a sensor device for giving a warning if fire breaks out. It may sense heat or smoke and will sound a siren or a bell to warn the occupants of the impending fire. It is recommended that every home have one smoke detector per floor.
History.
As early as 1851, an electric fire alarm was already invented by William Channing and Moses Farmer. There is little information to follow-up the development of the smoke detector or the fire alarm over the years. .
Then in 1970, Pittway Corporation purchased BRK Electronics from the original owners. During the early 70's, intense product development produced a series of high quality, affordable, battery and AC powered and system smoke alarms. .
In the following years, BRK Electronics introduced the FirstAlert brand for residential smoke detectors. By 1992, the company released a carbon monoxide alarm.
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How it works and illustration.
All smoke detectors consist of two basic parts: a sensor to sense the smoke and a very loud electronic horn to wake people up. Smoke detectors can run off of a 9-volt battery or 120 volt house current. .
Photoelectric Detectors.
Occasionally one will walk into a store and a bell will go off as he crosses the threshold. If he looks he will often notice that a photo beam detector is being used. Near the door on one side of the store is a light (either a white light and a lens, or a low-power laser), and on the other side is a photodetector that can "see" the light. When he crosses the beam of light he blocks it. The photodetector senses the lack of light and triggers a bell.
Photoelectric smoke detectors therefore use light in a different way. Inside the smoke detector there is a light and a sensor, but they are at 90 degree angles to one another, like this: .