Monitor My Interconnected Smoke Detectors?

Hardware
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Like many, the smoke detectors in my home are all linked with a 3rd (red) signal wire that ensure they all sound when any one of them detects smoke.

My home has Kidde detectors and my parents’ has First Alert detectors.

I am not looking to replace these with smart-home-friendly smoke detectors, just exploit what is already there. (When I did have a “smart smoke detector” from SimpliSafe, a weak battery triggered a false alarm while we were away. After that, I want to stick to solid, hard-wired devices from established brands.)

My first approach to bringing them into the Home Assistant ecosystem was to buy the relay module (Kidde , First Alert) which connects to the power and signal wires and operates a relay when the alarm is signaled. Then I’d wire a Zigbee leak sensor to the normally-open relay so it would report “wet” when the smoke detector wore off.

This is an almost “no-soldering” approach that I could package and put near any one of the ceiling mounted detectors. To keep it invisible, it’d probably have to go into the wall or ceiling.

While quick to assemble, my worry is that I don’t want to have to get back the to device to replace the batteries in the leak detector.

Recently, I’ve been mulling just using and ESP board, powered by a small USB adapter. Pretty straightforward to attach a GPIO to the signal line. I’m about to set one up on the bench to get a better read on the signal characteristics (voltage, polarity, timing, etc.) and set up the ESP to report alarm status.

Of course, this offers the (?dangerous?) opportunity to have the ESP activate all the alarms by driving the signal wire itself. (Use as auxiliary alarm for the home security system?)

I haven’t seen anyone tackle this yet… Hoping someone sees this post and has some information to share before I breakout the parts kit. Anything regarding the interconnect signal would be helpful. I found a couple articles (e.g. here, here) but actual reports or projects would be much more helpful.

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If you have Z-wave, this works great: Zooz ZEN55 DC Signal Sensor – ZOOZ

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Great suggestion! I have z-wave in one of the homes. zigbee and wifi in both.

Both houses are on the same wifi system (radio link). My zigbee controllers are ethernet-connected (POE). My zwave controller (zst39), however, is usb connected and won’t reach to the other home. My understanding is that the zwave integration talks to only a single zwavejs ui node.

I tried to get zwavejs to publish through mqtt, but it was impossible for homeassistant to properly discover my honeywell thermostat using mqtt. So I went back to using the zwave integration.

This is clearly 1/2 the solution. I’ll start digging for a zigbee equivalent. (Unless you know how to connect a 2nd zwave controller directly to ethernet or wifi)

One thing to confirm… that the junction boxes where the smoke detectors are mounted are plastic and not metal.

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Thanks PecosKidd

Installed it the other day and it’s working great. Took a small amount of fiddling to get the settings right, but that’s a lot easier than starting from scratch.

Now to figure how to handle the 2nd home - no z-wave there and still haven’t found a zigbee or wifi version of this device.

So I decided to say code-compliant. Bought a First Alert RM4 relay module. Would be easy to wire to a door sensor (replace reed switch) or leak detector, but I don’t want to have to go into the ceiling to replace batteries.

I settled on adaping an in-wall power module. It runs off A/C, so that means I will lose access in the event of a power failure. I wired the relay to the switched input and monitor the results in HA as if the light were manually turned on and off. Tried with both a zigbee and wifi (Sonoff Mini R2) module. Since the path to HA is shorter (presumably more reliable) with wifi than all the intermediate components in the zigbee path, I chose to reflash the Sonoff to ESPHome and use that.

If I ever worry about still operating during a power outage, I would investigate if I can make a parasitic power supply from the actual signal itself (somewhere in the 9V range). That would be pretty cool, but would definitely be violating code by putting non-approved equipment into the system.

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