History of the Photoelectric Smoke Detector

Invention

• The first patented electric fire alarm and detector was invented in 1890 by Francis Robbins Upton, an associate of Thomas Edison. The first electronic sensor to detect smoke was actually discovered by error. In the 1930s, a Swiss physicist named Walter Jaeger was trying to develop a sensor for the detection of poisonous gas. After one failed test, Jaeger lit a cigarette and the smoke tripped the electronic sensor, leading to the invention of the first electronic device for smoke detection.

Development

• The original mass-produced smoke detectors used ionization to detect the presence of particulates in the air, such as the kind produced by smoke. This type of smoke detector has an ionization chamber that contains two electrodes that measure alpha radiation as air passes through the chamber. These detectors contain the radioactive element americium-241 at low levels that create a flow of alpha particles between the electrodes. Smoke that passes through the air will interrupt this flow, setting off the alarm.

Photoelectric Cells and Smoke Detection

• Photoelectric devices for smoke detection were invented in 1965 by Duane Pearsall and Stanley Peterson in Lakewood, Colorado. Peterson developed smoke detectors for mass-production in 1975 for Pearsall's Statitrol Corporation. Photoelectric cells were later added as an alternative to the use of ionization as a means of smoke detection. The first smoke detectors for home use contained large batteries that were impractical to replace regularly, leading to the use of smaller AA batteries.

How Photoelectric Smoke Detectors Work

• According to the U.S. Environmental Protection Agency, photoelectric smoke detectors work on the principle of light beam interruption. These types of smoke detectors consist of a light source, usually white light or more often a low-power laser, and a photoelectric cell. The light beam is sent across the detector, with the cell usually set at a 90-degree angle to the light beam. When smoke particulates cross the light beam, the beam is deflected from its normal path and is directed at the photoelectric cell. This deflection to the cell then sets off the alarm.

Later Developments

• Concerns about the use of radioactive elements in smoke detectors, especially for home use, has led to the development of more affordable photoelectric smoke detectors. Although the levels of americium-241 present in most home smoke detectors have been considered to be safe, the possibility of long-term exposure to biohazards such as low-level radioactive elements has more recently caused concerns related to health issues. This has led to the increased interest in the development of less-expensive photoelectric smoke detectors that contain no radiation.