Integrating Kidde Smoke / CO Sensors into SmartThings Properly

[Navat604 (R.)]

@vseven

So you have two outputs off that Kidde relay, a set for normally open and a set for normally closed. You are using the normally open set to trigger your alert. However you can use the normally closed set also. The relay isn’t rated for the furnace load but a standard RIB should work fine. Wire the existing 120v hot to the kidde NC wire then your RIB “hot” to the common. Wire the RIB neutral to your 120v neutral. Your RIB should be ON since the Kidde NC is making the connection. Wire the relay side of your RIB to the power feeding the furnace.

On smoke the NC will switch to open cutting the power to your furnace. Under normal conditions your furnace will run like normal. If there is a issue with your smoke or you have the circuit turned off it will still run since it’s on the NC side.

Note: I’m not a electrician although I work in a field that has had me do lots of electrical stuff. You might want to run this by one you know (or maybe @Navat604 ?). Also you are sharing the common from the Kidde between your 120v and your EcoLink sensors input. In my industry this would be fine and “should” work. But if in doubt just buy another Kidde relay…maybe even run some 12/3 or 14/3 wire over to your furnace. You can have multiples relays on the same link since they are just listening for the signal.

Here is an awful picture in a attempt to describe what I’m talking about.

I wouldn’t have a wet contact connecting to the Ecolink sensor. Also installing the sensor in the same junction box as the smoke detector is also not a good idea. I can suggest something else though.
How about using a Vision single relay module instead? have the kidde relay dry contact trigger the Vision relay module. Use the dry contact of the vision module to control your furnace circuit. You can create a simulated smoke detector and sync it to the Vision relay for smoke detection. By going this route. You will not need the Ecolink and the RIBU1C and it’s much safer.

VISION - ZL7431US - Single Relay Module Switch - Wiring Diagram and Other Useful Information

I have been searching for a simple and tiny relay switch to use with Smartthings. I believe I have found it. I have been testing the device and created a Wiring Diagram that is more useful than the one supplied by Vision. This product was intended to be used behind non-smart wall switches to allow you to make a dumb-switch smart. This works in Smartthings without a custom device handler as a simple switch. If you change the device type in the IDE to say a Z-Wave Virtual Momentary Contact Switch then its applications open up tremendously. Also the RELAY on the Vision ZL7431US is isolated unlike the Fibaro switches I have tried. To me having the isolated relay makes this much more useful for other projects. Also because it is much more tiny than say the Linear FS20Z (also an isolated relay)…