It sounds like the setup to a joke. “What’s the difference between a hamburger and an armchair?” The consequences of the punchline are no joke. They could mean the difference between alerting you to a potential fire in the armchair or a false alarm from the cooking hamburger.

The reason is because not all smoke is the same. Different sources produce different types of smoke. Yet many smoke detectors can be just as easily triggered by a cooking hamburger as fire from a burning armchair. Tragically, unwarranted alarms, such as those from dad cooking a well-done burger, leads to almost a quarter of all smoke alarms to be disabled. With three out of five fire-related deaths coming from properties without working - or disabled - smoke detectors, there is an urgent need for these devices to produce fewer false alarms. The need is even more critical today, as the time needed to escape a modern home or building has been cut almost by half due to modern synthetic building materials which burn faster. When there really is a fire, people need confidence the threat is real, so they will react faster and get out of their building or home quicker. (In fact regulations, such as UL217, are continually being revised to ensure that regulated smoke detectors eliminate  false alarms and with increasingly faster alert times, depending on smoke type.)

To understand the breakthrough in smoke detection made by Analog Devices, we need a basic understanding of how a typical smoke detector works. Inside is a device called a photocell, made of material which conducts electricity. How much electrical current flows is directly related to the intensity of light shining on this material. So, when smoke passes between the light source and the photocell, current flow in the circuit changes - because the light is blocked - setting off the alarm.* The problem, as stated above, is smoke detectors cannot distinguish between smoke from a burning chair or a cooking hamburger.

ADI engineers did a deep dive into the problem and came up with a different way not just to detect smoke but detect different kinds of smoke. They did so by changing the frequency of the beam of light shining on a built-in photodetector. Then they literally went one better by adding a second beam at a different frequency. To analyze the two signals now being produced by the sensor a bit of programmable digital logic was added. Everything needed for a complete advanced smoke detection system is there in one package. The product is known officially as the ADPD188BI but is often called, because of its incredibly small size, by its nickname “Smoke Sensor in a Bottle Cap.”


ADI’s new smoke detection solution is small (3.8mm x 5mm x 0.9mm) and uses three times less power than existing solutions for longer battery life

The “bottle cap” part of this solution is a story unto itself. The only light you want shining on the photodiode must only come from the built-in light source. Any other light could trigger or, dangerously, prevent an alarm from sounding. ADI engineers designed a light-limiting cap to go on top of the ADPD188BI. It prevents light - other than the two internal beams - from hitting the sensor. To manufacture this cap, we turned to Accumold, an Iowa-based leader in moulding and packaging. Together Analog Devices’ ADPD188BI and Accumold’s 28800X smoke chamber are a UL listed solution to the armchair/hamburger problem.

For engineers who require a smoke detection solution unique to their needs, the ADPD188BI can be custom programmed to detect and alert different types and combinations of smoke. Developers are encouraged to visit the ADPD1881BI web page for all the details. There’s also a short video you can access near the top of a recent demonstration of the product in action.

Video with button

Video explaining how to set up the ADPD1881 Smoke Detector

The ADPD188BI Integrated Optical Module for Smoke Detection may not help dad cook a better hamburger, but it can make homes and buildings safer.


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*I cannot resist a quick aside about a Zurich patent clerk who was so intrigued by photocells he questioned the very nature of light. It basically boiled down to whether light was made up of waves or particles. The answer? It is both. Albert Einstein’s 1905 paper on light energy led to the development of quantum mechanics and would earn him the 1921 Nobel Prize in physics for "his discovery of the law of the photoelectric effect." A century later quantum mechanics is still used by scientists in their quest to understand the very nature of the universe.