Monitor Wired Smoke Detectors

I see from a recent blog post that battery operated Iris smoke detectors are compatible with ST.
Since no one appears to be making a wired version yet, is there a way to monitor the 3rd “trigger” wire on my existing detectors? As many of you probably know, a standard wired detector has a 3rd link wire that will activate all detectors if one goes off. It would be great to tap this wire and monitor it for change.

According to this page the 3rd interconnect wire sends a 9v trigger to the other detectors. I’m wondering if I hooked up a MIMOlite, that ST could be programmed to handle it appropriately.

I have read either on this forum or somewhere else that purchasing the add on relay like the Kidde SM120 will allow the connection of a device such as a door sensor to be added. You just have to find the one designed for your system.

I have ordered this relay already and will report back my findings soon.


Here is a thread on doing just that. It works like a charm:

Thanks @kg4fku and @trotsky40, I think this is a nice little solution. The only thing that bugs me about all the “things” is battery replacement. I was hoping with the MIMOlite it would be hardwired and I could forget about it.

@trotsky40, did you get it to show up in the dashboard as a Smoke Detector or is it a door contact? I really want it to be in the Damage and Danger section so I get the appropriate alerts and UI.

It doesn’t show up on the Dashboard but I haven’t played around with it since the Dashboard came out. If I get some time this weekend, I will see if I can get it to show up (my programming skills are limited).

I solved this last night.
I used the exact same setup: Smoke Alarm Relay Accessory kit, RS100HC. What I added was a AC power supply into the mix.
It was a small 3V supply that came with some small LED lighting.
I took both the supply AND the RS100HC out of their cases, desoldered the battery terminals, and soldered the power supply wires directly to the RS100HC.
After plenty of electrical tape as insulation I stuff the entire package into the same ceiling box as an existing smoke alarm. It is important to use choose a smoke alarm is at the END of the chain, otherwise there are too many AC wires in the way. The end chain smoke alarm will have only 1 AC wire entering the junction box, vs two (or more).
This makes it possible; otherwise there will most likely not be enough room.
Now the battery indicator always shows 100%.
Minor issue is the RS100HC shows that it’s covered has been removed, but again its minor; Events still process properly.

The last thing I still want to customize is the software; It shows a door (open / closed). I would like it to properly show a Alarm inside the SmartThings software. Not a deal breaker but a nice to have.

Its good to know that one can detect that the smoke alarms were tripped while away.

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Glad you were able to get your system working the way you wanted.

I plan to keep my system battery powered as I want to be notified of smoke/fire even if main power is lost. My SmartThings hub resides on its own UPS so it always has power. I designed my system this way because we can lose power at anytime and I need to know if my backup systems have started remotely and, if not, are there any issues in the house like smoke, fire or flooding.

You could have expanded the battery pack to give a longer life span. I test my detectors once a month and replace batteries as needed.

You bring up a good point.
I believe AC wired interconnected smoke alarms do not trigger one another while there is no AC power.
Once they are on “battery backup aka 9V battery” they behave as simple “dumb” smoke alarms.
The alarm accessory relay needs AC power to trigger the relay in the first place…
In theory, the alarm accessory relay may never trigger the sensor at all!

You should test this on your system.
I cannot since my sensor is now AC powered as well.
For a backup plan, you could install the First Alert Smoke and CO Z wave alarm (completely battery powered).
I installed one in my basement, and I may install another one on my top floor to supplement the hardwired smoke detectors.

The KIDDE interconnected systems do trigger all interconnected items on 9V battery power. This is actually one of the tests preformed once per month to ensure proper system operation. Not sure if any other manufacturer of alarms have this ability as I only have the KIDDE system in my home.

Thats good to know about the KIDDE systems.

But what about the SM120x?
Does that still work without AC power?

From everything I have read and the documentation that came with the unit it should work. I will let you know soon once I have it installed.

SM120X will not work without AC power

Thanks doc, unfortunately that is what I suspected. It’s not still you start to think about all the use cases you realize all it takes is one item to knock out a whole chain.

I am going to get a second Z Wave (IRIS) First Alert Smoke Alarm/CO detector (battery operated) and use that a backup in case of power failure.

I have posted some code using the SM120X and the MIMOlite to sense and trigger wired smoke detectors.

I have a mixture of Kidde connected wireless and wireless only smoke/CO detectors. I’m thinking of getting a wireless only and gutting it to interface to the ST with a contact sensor.

Actually, I just thought of another idea. If It get the Kidde wireless and interconectable I can modify it so that I can use the trigger to turn on a 120V relay which when connected to a contact sensor (or mimolite) I can integrate with ST. I an also connect to the DSC panel to tie to the alarm panel