How to wire relay to ecolink sensor?

This has to be a dumb question, so I apologize. But every post I’ve found about connecting a relay to an ecolink sensor simply says “wire the relay to the sensor inputs” but I can’t find anything that tells me specifically which wire goes where. I have opened up my ecolink door/window sensor, and I see two input contacts, but they are not labeled, and they are also not identified in the documentation.

So I have a BRK RM4 relay with a brown common output, a blue NO output, and a gray NC output. I know I don’t need both the blue and the gray wires, but which wires do I put into which inputs? I have no idea, and I don’t want to risk frying my sensor.

Thanks in advance for any help!

It shouldn’t matter which contact you hook to on the sensor. You are just completing an open circuit. You would hook your common to one of the terminals and either the NO or the NC to the other contact depending on your needs. Make sure you don’t hook the sensor contacts to any power source.

What are you working on? I used an Ecolink tilt sensor and a magnetic reed switch for my mailbox sensor and it has worked perfectly for many months now. I’m curious as to what you are doing with the relay.

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).

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.

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Haha. I knew it was a dumb question! It didn’t occur to me that, since it’s just a switch, it doesn’t matter which wire goes where. Thank you for pointing that out!

So I just put the common wire in one of the inputs and either the NC or the NO wire in the other input, depending on which driver I want to use, and then I cap off the wire I’m not using…correct?

As for what I’m doing, we are building a new house, and it has interconnected FirstAlert Smoke/CO alarms. So I had the electrician run the Smoke alarm circuit and interconnect wires to a box in my “Internet/Smart Home closet”. I’m planning on hooking the BRK RM4 relay up to the circuit and the interconnect wire, and then to the Ecolink Window/Door Sensor, so alarm signals will go to my SmartThings hub.

Thanks for the help!