The low-cost, reliable, ubiquitous smoke detector is an example of complex physics and optics made real by semiconductors.
We’ve come to accept the basic residential smoke detector, which retails for just $15 to $30, as a standard home-safety accessory. Most building codes now require these in or near designated areas such as the kitchen, bedroom hallways, and basement for a certificate of occupancy and insurance coverage.
And why not? They are inexpensive, reliable, and effective. While many statistics on house fires and meaningful historical data are difficult to assess, the overall trend in such fires is definitely down (Figure 1).
Of course, there are many reasons for the change in the number of house fires, and it is hard to disentangle, compare, and normalize them to reach definitive correlations and conclusions. On one hand, factors such as reduced smoking and better wiring codes likely contribute to a decrease. On the other hand, an increase in the number of houses (dwellings) and population, people at home more, and other hard-to-measure items may have the opposite effect.
According to the Federal Emergency Management Association, the top three causes of fires in homes are cooking, heating equipment, and electrical malfunction. Further, small “trash can” fires people put out on their own, often with an extinguisher, may not be reported. It’s a very complicated data situation.
Of course, smoke detectors do not stop fires from starting, but they do reduce the severity of the associated damage and injury (including death) of the fires since they detect fires earlier; there’s no doubt of that. Further, smoke alarms save lives. According to the National Fire Protection Association (NFPA), working smoke alarms in a home reduces the risk of dying in a fire by 55%.
This FAQ will look at the basic smoke detector and how to implement this physically small, high-volume consumer product, which is a largely unappreciated “miracle” of modern technology. It will also look at recent developments in advanced technologies targeting commercial and industrial environments.
Q: What is a smoke detector? Is it the same as a fire detector?
A: A smoke detector is just that: a system for sensing the presence of smoke. But as the saying goes, “where there’s smoke, there’s fire.” In most residential (non-industrial) settings, smoke particulates in the air can be detected sooner and easier than the heat of a fire, so a smoke detector is an early warning system. However, it can also mislead s since particulates due to heavy dust, cooking fumes, and similar can set off the smoke detector. Note that the better and preferred name for a smoke detector is smoke alarm since it both detects and warns (Figure 2).
Q: Do houses have fire detectors rather than, or in addition, to smoke detectors?
A: Generally, they do not. By the time the heat of a fire reaches the detector, the fire is usually well underway. Nearly all residential fires generate significant smoke, unlike some industrial and laboratory situations where you can have a fire with little or no smoke. So it’s much more meaningful and beneficial to sense the presence of smoke in a residence rather than the heat of a fire.
Q: What is the history of residential smoke detectors and alarms?
A: In a word, it isn’t very easy. Smoke detectors are we know them began appearing in the late 1950s to 1970s. Wikipedia has an interesting discussion with references but also acknowledges there are disputed statements and specifics.
The next part of this article will look at the operating principles of smoke detectors.
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Free-space optical links, Part 1: Principles
Free-space optical links, Part 2: Technical issues
Free-space optical links, Part 3: Standard units
- National Fire Protection Association “Smoke Alarms in US Home Fires”
- The Zebra, “House Fire Statistics in 2022”
- NIST, “How Do Smoke Detectors Work?
- S. Fire Administration, “USFA position on home smoke alarms”
- National Fire Protection Association, “Ionization vs photoelectric”
- Wikipedia, “Smoke detector”
- Statistica, “Total number of reported home structure fires in the United States from 1977 to 2020”
- IFSEC Global, “Smoke Detectors Explained”
- IFSEC Global, “The science behind optical beam detection in large, open spaces”
- IFSEC Global, “FFE launches auto-aligning smoke beam detector”
Integrated Circuits – Vendor web sites
- Analog Devices, “Smoke Detection”
- Allegro Microsystems, “Smoke Detector Interface ICs”
- Microchip Technology, “Smoke Detector, CO Detector and Horn Driver ICs”
- NXP/Freescale, “MC145010 Photoelectric Smoke Detector IC with I/O”
- Renesas, “RAA239101 Photoelectric Smoke Detector AFE IC”
- Texas Instruments, “Smoke & heat detector Products and reference designs”