When: 1965
Where: USA
Why: The smoke alarm has revolutionised safety alert systems and saved lives
How: Adding batteries and an audible alarm to early conceptual work made the smoke alarm suitable for the residential market, and therefore for mass consumption
Who: Duane Pearsall and Stanley Peterson
Fact: Many modern smoke alarms use the same type of radioactive material as is used in the space programmes
This palm-sized life-saver is discreetly located in the majority of residential and commercial properties today. Tucked neatly out of plain view – generally on walls above eye level, or on ceilings, the smoke alarm or smoke detector is one modern safety device that no home, office, restaurant, hotel or establishment should be without.
Fire detection has changed radically over the years – 200 years ago the method of alerting of the danger of fire involved banging on doors, blowing whistles, ringing church bells and even shooting into the air with a gun. Thankfully, times have changed, and in the lifespan of the humble smoke alarm countless lives have been saved. As inventors develop and hone the device to produce updated models even more effective in detection, the smoke alarm’s invaluable work looks set to continue.
The history of the smoke alarm began with the US inventor Francis Thomas Upton, who created the first fire alarm in 1890. The patent number for this first device was 436,961. However, the invention was very basic and little interest was shown in the product. Upton’s model was soon replaced by new models, the next one of which was created through a lucky accident.
The succeeding smoke alarm was invented by chance in 1930 by the Swiss physicist Walter Jaeger. Jaeger was attempting to invent a sensor that would detect poisonous gas. His idea was that the gas would enter the sensor and ionise the air, causing the meter current to be altered. However, the gas was ineffective in registering in the current meter on the device. Jaeger, believing that he had failed, took a cigarette break. Not long after lighting his cigarette, Jaeger noticed that the meter current on the detector had dropped and he discovered that it was smoke that the sensors had detected, not gas. This breakthrough moment revolutionised the future invention of smoke alarms. Nevertheless, it was not until more than a quarter of a century later that smoke alarms were developed for the consumer market.
While these early devices hardly made a commercial impact, the scientific ground work conducted by Upton and Jaeger paved the way for successive smoke alarm inventors.
Not long after lighting his cigarette, Jaeger noticed that the meter current on the detector had dropped and he discovered that it was smoke that the sensors had detected, not gas.
Manufacturing remained very expensive for the next three decades and it wasn’t until the mid-1960s that affordable smoke alarms could be mass produced. The first few smoke alarms that were available were so expensive that only large companies could afford to install them.
The first battery-powered smoke alarm was developed by US inventors Duane Pearsall and Stanley Peterson in 1965. Their design was operated by batteries, which made it cheaper and easier for home owners to run them, and from the late 1960s onwards, smoke alarms were produced for the residential property market. However, Pearsall and Peterson soon noticed a flaw in their first model. The original alarm contained large batteries that were expensive and impractical to change regularly, which led to the invention of a model that made use of smaller, AA batteries, making it more commercially viable. Both of these models were made of metal and were resistant to fire. The battery was made by Gates Energy and it wasn’t long before the heavy-duty rechargeable batteries were replaced by single-use AA batteries.
The devices proved very successful. In 1975 Peterson and Pearsall began mass producing their devices under the company name Statitrol Corporation and became the first in the history of smoke alarms to sell the product commercially. By 1977, the company was shipping 500 units daily.
However, in 1980 Statitrol had sold its invention rights to electronic goods manufacturing giant Emerson Electrics. Later, the US manufacturer Sears would end up selling the product, which remains popular today.
The audible alarm quickly emerged as the most popular type of device. The alarm sends out a high-pitched beeping or ringing noise, and is activated when smoke is detected, thus causing a fire alert. However, consumer demand and a drive for difference has led to the evolution of the simple smoke alarm and now a plethora of alarms can be purchased that are specifically designed for the needs of the hard of hearing or the visually impaired, which use strobe lights or a vibrating action to create the alert.
Many modern smoke alarms use the same type of radioactive material to detect smoke particles as the silver foil used in the US space programme. This type of smoke detector is known as an ionisation chamber smoke detector (ICSD) and is quicker at sensing flaming fires that produce little smoke. The ICSD was invented in Switzerland in the early 1940s and was introduced into the USA in 1951. It uses a radioactive material to ionise the air in a sensing chamber; the presence of smoke affects the flow of the ions between a pair of electrodes, which triggers the alarm. However, use of this material been questioned in recent years because concerns have been raised about the long-term health implications of exposure to a radioactive biohazard.
Although the levels of americium-241 present in most home smoke detectors are considered to be safe, the possibility of long-term risks has led to the development of photoelectric detectors, which contain no radiation and are in fact more affordable. Photoelectric detectors use an optical beam to search for smoke. When smoke particles cloud the beam, a photoelectric cell senses the decrease in light intensity, which activates the alarm. This type of detector reacts most quickly to smouldering fires that release relatively large amounts of smoke, and has proved to be a popular alternative.
Many modern smoke alarms use the same type of radioactive material to detect smoke particles as the silver foil used in the US space programme.
The smoke alarm is one invention that has stood the test of time. It is now a legal requirement for all commercial buildings and rented accommodation in the majority of developed countries to be fitted with a fully functioning smoke alarm. This is particularly important as the electronic equipment we use on a daily basis increases. In the USA, 96% of homes have at least one smoke alarm, according to the National Fire Protection Association, but many people fail to test that their alarm is working regularly or to change the batteries. According to the London Fire Brigade, while 85% of UK homes have an alarm fitted, many fire-related deaths are caused by people being overcome by smoke and fumes, not just by burns, which is why newer models are being developed that detect the presence of smoke at an earlier stage.
The smoke alarm has undergone several transformations and has come a long way since its accidental beginnings. While many of the earlier smoke alarm models were prone to giving false alarms, models today have developed and come with features that aim to reduce the occurrence of false alarms.
The smoke alarm is one invention that has stood the test of time. It is now a legal requirement for all commercial buildings and rented accommodation in the majority of developed countries to be fitted with a fully functioning smoke alarm.
However, as a health and safety device the models we use today are in a constant state of evolution, as product inventors and designers continue to experiment to create prototypes that are even more effective in detecting smoke and saving lives.
Following in the footsteps of Upton is an award-winning young British teenager called James Popper, who came up with an idea for an infrared detector that identifies fires in their infancy. Popper had the idea after a fire destroyed the kitchen of a family friend, leading him to invent the CookerSmart IR Kitchen Flame Detector, which reads the specific infrared frequency bands of flame. While this model of alarm is still relatively new to the market, it appears that it won’t be long before new technologies take its place.