How to wire relay to ecolink sensor?

[MarkTr]

BRK RM4 is a smoke detector relay. Whether you connect NO or NC depends on what device handler you used. If you use NO, the sensor will read as “open” until the alarm is triggered, then the relay will activate, that contact will close, and the sensor will change states. If you use NC, the sensor reads as “closed”, and opens on an alarm signal, again changing the sensor state.

The handler below includes a toggle; just pick one wire to connect, and if it doesn’t work as expected, flip the toggle (reversing the connection in software vs hardware).

Integrating Kidde Smoke / CO Sensors into SmartThings Properly

I looked up that relay and the brown is supposed to be “common” and the blue is supposed to be normally open, so it looks like you have it wired right on that side, assuming you have it wired right to the smoke detector. The only thing that makes sense to me is if it’s wired backwards on the smoke detector side but it doesn’t really sound like it. What you probably should do is meter your relay outputs and see what you have and when. In the meantime, you can use this device handler if you want. It’s based on vseven’s handler which I used initially, then built my own for a different purpose. But the advantage it has is in the preferences, there’s an input toggle. So whether you have it wired normally open or normally closed doesn’t really matter - you can just flip the toggle if you’re no…

I’m not an expert but I’m guessing it would be considered more “fail-safe” to use the NC connection. That way if something causes a loss of signal from the alarm/relay, ST is immediately triggered, whereas if you use the NO connection, the problem is hidden until the alarm goes off and ST fails to see it.