Connected Smoke Alarms

Yes that is correct. When I bought my house I only had 1 wired smoke detector in my upstairs hallway. Code in my area has changed and now requires smoke detectors in all bedrooms. When I was renovating my kitchen I didn’t want to get caught up in all of that and have to pay an electrician for something I could do so I installed a wired smoke detector in all bedrooms and connected them to the hallway smoke detector in parallel: hallway to bedroom 4, bedroom 4 to bedroom 3, and so on. Then I found a way to run the wire from the attic to the crawl space below the first floor so I removed my downstairs battery hallway detector and connected it with a wired one. Long story short I knew how it was all wired together and I had easy access to the last run. The bedroom detectors are just smoke and the hallway are combination smoke and CO, all Kiddie brand. I am adding on to the back of the house which will require another smoke detector so I wanted to get this done prior and have room to add another 14-3 Romex into the box.

Since the downstairs hallway detector is at the end of the run, I ran another 14-3 Romex up into that junction box and then down into my crawlspace into 38-cu double gang box:

This particular box was the only one I could find that would fit both relays:

  • The Kiddie relays are quite long and I didn’t want to bend the wires too much
  • I wanted to have room to easily add another 14-3 Romex for my new smoke detectors with my addition
  • The back of the box is flat and requires that you use wire connectors to secure the wires coming into the box.

As mentioned above I took both relays into Lowes and tested each box until I found a fit - of course I had to explain what I was doing to the electrical dept employee since I was on that isle for quite a while. Lowes nor Home Depot carry the Kiddie relays so I just purchased from Amazon. For those of you with First Alert, I believe Home Depot may carry at least the smoke relay.

You will see the black SM120X in the back and the purple CO120X in the front (the CO120X is a little longer than the SM120X). On the right I put a 3/4 wire connector that the Romex wires will run though and into the box. Then on the left I have a 3/8 wire connector that the low voltage relay wires run out of and into a single gang box next to it. I bundled together the Romex red, black, and white wires from the smoke detector with the red, black and white wires from the relays and put a wire cap on them. The ground wire from the smoke detector is not used and is just tucked away in the back.

I have plenty of room to the right of the relays for additional wires. The SM120X does have a 9V DC output to power another device. I am not using that so I just tucked it in behind the relays and the only wires going out into the single gang are the low voltage NC, NO, and Common wires from the relays. The 9V DC output could be used to power an Arduino or something in the future ;).

In the single gang box, I connected the NC and Common wires to a small piece of 24-2 security wire I had laying around. This wire’s diameter is much smaller and easily fit into the Ecolink or Schlage contact sensors without additional drilling or alteration. You can easily use telephone wire or something small. Since I prefer to have the normal state of my contact sensor be “closed” (NC) and when tripped “open”, I just wire capped the NO wires and left them in the box. But if you prefer to have normal state be “open” and “closed” when tripped you can choose to use the NO wire instead but point being is you only need to use the common wire and NC or NO, not both.

I wanted the ability to change the contact sensor battery without having to open a gang box. I purchased a blank wall plate and drilled holes to hold the contact sensor mount and drill extra holes to run the 24-2 security wire through that is connected to the contact sensor. Both the Ecolink and Schlage contact sensors have wire terminals inside. There are reports that the Schlage doesn’t report battery, but my Ecolink appears to, though I am not 100% sure since it is still on 100% - at least I got a value of something so hoping it works.

And finally here is the finished project all closed up:

I added both contact sensors to SmartThings BEFORE installing them under the house to make sure they worked with just the magnet. Once installed I ran a zwave repair since the location changed. I ended up cloning the zwave contact sensor device handler and made my own so I could change the words “open” and “closed” to smoke/no smoke and co/no co and I also changed the image to a smoke detector.

Each time a push the test button on a smoke detector, the smoke relay will trip and report Open, though re-labeled to “Smoke”. When I press the test button on a smoke/CO combination both the smoke AND CO relays trip and reflect an open state.

Something I may consider in the future is wiring the smoke relay into my home security panel since that is also supported too.