Housing room node in smoke detector

[Zeph]

This idea derives from another thread (on Audio/Visual alarms and deterrence).

What about housing a typical room node in a hacked smoke detector? For example, Temp, Humidity, Light sensors (maybe even motion) - plus the smoke alarm detection itself, and perhaps make the buzzer an actuator.

As I said in that thread, I might keep the detector directly connected to the buzzer, just for safety, but it might be possible to also actuate the buzzer from the uC.

This would not only add a useful sensor (networkable smoke alarm) and possibly actuator(buzzer), it would mean no extra visible box for the room node - we take the smoke detectors for granted and barely notice them.

Has anybody tried this yet?

(I'm heading out shortly for a decidedly non-electronic weekend myself, but I wouldn't be surprised if a few smoke detectors get opened this weekend by our more intrepid explorers)

[Yveaux]

@Zeph said:

if a few smoke detectors get opened this weekend

Do you really think I didn't take one apart yet?

[epierre]

well I would be interrested, I guess they are optical, not electrochimical... but I don't imagine which composants could do this, any idea ? (Mr Box Opener

[Yveaux]

@epierre said:

I guess they are optical

Some use ionization and are radioactive... Don't take apart the actual sensor!

[epierre]

@Yveaux but do you know some that could be used to make it, the safe way ?

[Yveaux]

@epierre To be safe, go for the optical ones if you want to hack.

Just to give you an idea what the radioactive chamber looks like (in fact it looks identical to the ones I took apart in the past):

Radioactive Americium 241 – 04:01
— David Rutherford

[Zeph]

We have no need to open the sensor per se, just the outer case - so a Americium Dioxide detector and/or photoelectric should be fine, no safety issue.

Connections to figure out:

Function 1: reporting a detected fire to the HA system - perhaps could tap into some signal from the sensor to the control circuitry, but I have no idea what that is (eg: an analog voltage read by an embedded uC?). Or just detect the siren going off, or an LED being lit, which should be easy. The idea is of course to not interfere with the normal function, just detect.

Function 2: externally triggering the alarm - eg: to scare away a burglar (or to network the smoke alarms). Either send the appropriate signal to the sound transducer module (eg: piezo buzzer or speaker) -perhaps just power if self-contained, or perhaps a square wave if the transducer needs it - or trigger the test button.

Function 3 - power. Would be nice to use the same battery.

Then add the uC and radio, and any other sensors (Temp/Humidity, light, motion, etc).

I'm guessing that one of the steps would be discovering a fire detector with enough room in the case. I'm thinking that one powered by 2xAA would be preferable to one powered by 9V, for battery life given the additional drain of our added electronics and sensors..

[RJ_Make]

I suspect for those with 120v interconnect detectors, you could use the interconnect signal for detection and perhaps automation.

This method is using the LED.

[Zeph]

Here's another project which passes a fire detection to a Home Automation System, much as I'm suggesting: http://harizanov.com/2014/07/diy-internet-of-things-fire-alarm/

The idea I was exploring is including our other sensors in the same housing if possible, and also making the piezo speaker a controllable actuator within our network.

I don't have a 120V interconnected system (sound nice tho), but that's a good option for detection for those who do. Another option for interfacing a Home Automation system with multiple networked alarms - like the battery powered First Alert OneLink system - would be decoding the 433 MHz signals passed between these alarms.

That of course does not take advantage of "hiding" a MySensors multi-sensor node inside the housing of a smoke alarm, tho. I kind of like the option of not needing to explain what these new boxes are in every room - if the sensor nodes look like smoke alarms, nobody will even notice them. And if that's done by making them hidden additions inside real and still-functioning real smoke alarms, even better!