PurpleAIr fire sensors dotting San Diego’s North County

Steve Sedio installing sensor

Steve Sedio installing sensor

On June 25, Steve Sedio noticed a fire blazing in Carlsbad about 30 miles west of his Valley Center home. “An arsonist started the brush fire in Carlsbad,” he told me on July 9.

The thing is, he didn’t see the smoke billowing from his vantage point, nor smelled it, yet. Instead, he monitored the fire and its smoke blowing towards him via three PurpleAir exterior smoke detectors, which relayed the intel back to an iPhone and Android app he is currently enhancing.

Fire sensors covering West Valley Center

“I collected data from three PurpleAir sensors,” he continued. “The first was 3.6 miles from the fire and indicated the fire started at 1 pm, which peaked at an air quality of 450 EPA PM 2.5 AQI. So it was really bad.”

EPA is the acronym for Environmental Protection Agency; PM is particulate matter; AQI, air quality index. The higher the AQI value, the higher the air pollution; AQIs registering between 301-500 are hazardous.

Sedio then noticed a sensor 14 miles east of the fire, slightly east of the I-15, which peaked at 171, “unhealthy” for certain dwellers sensitive to smoke but “a false positive alert with no fire nearby,” Sedio added and elaborated more on later in the article.

Then, about two hours after the Carlsbad fire started, he smelled the traveling smoke reaching his Valley Center home. “I checked our network, and most sensors were above 100.”

By now, the fire department had put out the fire in Carlsbad.

“And that shows how the system works,” Sedio explained. “With fires, I will look at two sensors several miles apart to see what direction the smoke is moving and how fast.”

Had the sensors’ readouts increased and reached 300 and higher AQI levels as the Valley Center fire did in 2003, which Sedio recalls killed two people. “When the app alerts you: go outside and look,” he forewarned. “If you see fire and you are at risk, leave and call 911.”

“I have been through three wildfires here, two of which started and required evacuation in the middle of the night. I’m an engineer who solves problems and have been looking for this type of system for 15 years, since the last fire in 2007. What surprises me is I can only find one startup company in Europe working on wildfire detection.”

Sedio’s June 25 Carlsbad-arson assessment was solely based on three PurpleAir sensors. He’s hoping with multiple units spread throughout his once-uber-rural community — he’ll help our first responders and residents efficiently detect the direction of spreading fires from miles away.

Since last month, his son, Vince Sedio, CEO of Valley Center Wireless, an internet service provider in the area, sponsored ten PurpleAir exterior smoke detectors for Valley Center inhabitants with available backup power. The older Sedio installed the $260 units apiece free of charge.

Sedio installed the sponsored PurpleAir units in crucial parts of the city affected most by the rolling SDG&E blackouts. Without power, the WiFi signals will seize, preventing on-the-second intel on the direction the fire is spreading.

Valley Center is located 10 miles northeast of Escondido, which already has a handful of PurpleAir sensors installed. The more PurpleAir exterior smoke detectors the community has in place, the faster first responders, Sedio, and his neighbors will be able to track the fire’s direction and spread. As a former electrical engineer by trade, Sedio prefers the PurpleAir sensors as the U.S. government follows them at Furthermore, the sensors are vouched for being resilient, so much so that others in Sedio’s Facebook group are shelling out $260 per unit and capitalizing on Sedio’s offer to install the units gratis.

Jim Davidson, Valley Center’s fire marshal, said in a recent Roadrunner interview, “The system that Steve [Sedio] is working on has [favorable] applications at times when cameras are not particularly effective at seeing smoke – like at night. The challenges are many, however. There is no way to discriminate between the smoke of a cooking fire or a wildfire. Determining the location of the fire from just smoke detection is a huge challenge as well. I can’t say how successful this system will be. But I can say that in a scientific endeavor, even failure is a success because of what we learn. And we will learn a great deal from this system.”

Regarding the campfire and chimney smoke in the area, Sedio collaborated with an app developer to help the Valley Center residents discern between friendly smoke and possibly dangerous warning smoke — but multiple sensors must be deployed in an area to help people decipher. “A key indicator of a wildfire is more than one sensor going off,” Sedio explained. “They are too far apart to react to a small fire. Also, we needed some way to automate an alert when one or more sensors reach the users’ set threshold [amounts]. Unfortunately, none of the existing apps associated with the PurpleAir sensor were adjustable” — which means they were set to a certain amount that could easily be triggered by something as innocent as a S’mores shindig.

“Kathleen Bonnet understood the project and agreed to modify her app — AQI SPY on Android and iPhone — for a very reasonable price. This [programming enhancement] was funded by Valley Center Wireless.”

Since setting thresholds of fire detection sensors via an app is the “first of its kind” in the market, to activate the unique feature “requires an upgrade to premium on the AQI SPY app, which is an $8 one-time fee,” Sedio added. “Which goes to the app store and Kathleen, the app developer.”

The retired engineer turned inventor studied the airstream and natural smoke streams in Valley Center and its surroundings depending on the time of year — for the last couple of years. From the numbers gathered, he adjusted the fire detectors’ optimal AQI threshold numbers concerning proximity to areas prone to nonthreatening higher AQI numbers. This includes sites closer to the July 4th firework shows, BBQ and fire pits, and clusters of homes and cabins with chimneys. Not to mention sections where controlled burns are initiated to eliminate dead trees, tree limbs, dried-out leaves, and debris.

Once the user invests the $8, the user can add as many sensors as they want, with each sensor set to whatever AQI threshold they desire; once a sensor is triggered, it’ll notify the user, but the information will also be posted on the community network.

“This is another piece in our battle with fire,” he said. “As we identify weaknesses in this system, we will resolve them or work around them.”

One apparent weakness is power outages or lack of WiFi, but Sedio has come up with a stand-alone design in case. He designed a unit that cost less than $500. The stand-alone smoke detector includes a T-Mobile WiFi hot spot from Amazon for $25; a solar panel and solar charge controller with two USB outputs — one for the sensor and the other for the WiFi hotspot, which runs $50; a 12V (10AH) LiFePO4 battery which costs $60; and a waterproof box that costs $40. The PurpleAir sensor is $260. “The data usage is low, so a $5 a month 500Mb plan from T-Mobile works fine,” Sedio added. “I have been running one stand-alone for about a month; the winter rains will let me know if I need a larger solar panel, maybe a 50W that’ll cost $60,” still keeping the stand-alone unit under $500.

Sedio suggested residents subscribe to the Brush Fire Partyline / San Diego North County and Brush Fire Partyline Alerts & Information — San Diego Area Facebook pages to cross-reference any possible fires in the area.

Then, he said to utilize the AlertWildfire cameras to look for signs of smoke. AlertWildfire cameras were mounted by the University of California San Diego, amongst other universities, to assist firefighters and first responders.

As this article goes to print on July 12, Sedio has a sitdown with the fire department. “I will show them how to use the PurpleAir real-time maps and fund the app’s purchase for their staff. The network is functional now. I will watch it during power shutdowns to see if we need to make any changes.”