Audio-coupled Smoke Alarm Interface Sends Texts, Emails

The Internet of Things is getting to be a big business. Google’s Nest brand is part of the trend, and they’re building a product line that fills niches and looks good doing it, including the Nest Protect smoke and CO detector. It’s nice to get texts and emails if your smoke alarm goes off, but if you’d rather not spend $99USD for the privilege, take a look at this $10 DIY smoke alarm interface.

The secret to keeping the cost of [Team SimpleIOThings’] interface at a minimum is leveraging both the dirt-cheap ESP8266 platform and the functionality available on If This Then That. And to keep the circuit as simple and universal as possible, the ESP8266 dev board is interfaced to an existing smoke detector with a simple microphone sensor. From what we can see it’s just a sound level sensor, and that should work fine with the mic close to the smoke detector. But with high noise levels in your house, like those that come with kids and dogs, false alarms might be an issue. In that case, we bet the software could be modified to listen for the Temporal-Three pattern used by most modern smoke detectors. You could probably even add code to send a separate message for a CO detector sounding a Temporal-Four pattern.

Interfacing to a smoke detector is nothing new, as this pre-ESP8266 project proves. But the versatile WiFi SoC makes interfaces like this quick and easy projects.

18 thoughts on “Audio-coupled Smoke Alarm Interface Sends Texts, Emails

  1. Given how cheap the basic smoke detectors are, wouldn’t it make more sense to modify one and use it in addition to all the unmodified units already in place? You could even place it in the kitchen to get an early warning. (Interesting note: some alarm companies specifically disallow connected smoke detectors in kitchens due to all the false alarms.)

    1. Also the other way around, dust and grease from cooking builds up in the sensor, preventing the detector from detecting smoke. So if you have one in the kitchen, you should either replace, or test it (with real smoke) frequently.

    2. Definitely a good point. I thought of this, but the central conceit of the tutorial is that this device can be made without complicated soldering. Its literally a plug and play device which can be completed by anyone who can install programs in a windows environment. Also, since it uses free cloud based services, you won’t have to pay monthly alarm company fees or be limited by their terms of service.

      From a technical point of view, modding an existing smoke detector will be challenging because the amount of power the wifi chip requires is non-trivial and will seriously reduce the battery life of the device. I’d recommend using corded mains power for both the chip and the smoke detector, and using the electrical signal for the piezo buzzer to trigger a GPIO pin. Definitely would be a cool hackaday project.

    1. Yes, wifi is not 100% reliable. Then again, if your smoke alarm goes off when you’re on vacation, having no cloud based notification at all is REALLY unreliable. At that point you’re hoping neighbors or the fire department will notice a house on fire before everything is literally toast. Yes, home security systems are available, but they are also expensive. My thinking was, its better than NOT doing it. At 10 dollars and about 30 min of work, its worth it.

  2. I was about to build something similar. Another sensor would be placed on the inside of the external wall on which I had the house alarm siren.
    I was considering using a piezo electric sounder as a mic though.

  3. the detectors in my house are ganged together. When one gets a signal that smoke is present, all begin to alarm. I haven’t reverse engineered or researched the brand to determine how it does it over conventional house power lines (the only interconnect between them and not limited to just the detectors, these circuits feed other home items). If I could decrypt that I’d pull in that info and use it in home automation.

    While WiFi isn’t ideal for disaster communication, if you consider that it’s unlikely to consume the entire domicile in one burst, it’s better than nothing.

    1. Your smoke detectors are likely hard wired to line voltage (110 volt AC). They used 3 conductor plus ground wire – black is hot, white is neutral, red (usually, or whatever color is left) is interconnect, and bare wire for ground. From what i have read, when a smoke detector goes off, it will either pulse or solid 9v DC through the interconnect wire to cause the others to sound.

      I read somewhere on some Z-Wave forum about interfacing a Z-wave switch to allow a smoke detector to send a signal through Z-Wave. Also on the same lines, using a Z-Wave outlet or relay with a 9v power source to create a “whole house alarm” of sorts, to be triggered by Z-Wave profile.

    2. Back in the day when these first came out in the UK I remember seeing some which daisy chained with standard alarm cable. Battery powered units. Some also had spot lights in them. The idea being that they would light the safe path to your exit.
      At the time, all smoke alarms were expensive. I think my dad paid about $100 for one. Today I can get one for $8 from the supermarket.
      I feel old…

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