Carbon Monoxide Detector Recommendation

I’m trying to identify the best solution to receive carbon monoxide alerts via home assistant.

BACKGROUND
My current setup consists of a mixture of hardwired and wireless interconnected First Alert Smoke Detectors with two combo Smoke/CO detectors in the mix.

My plan is to wire a Kidde SM120X relay into the interconnect circuit to trigger a zwave door sensor to get me alarm status. For other’s information: First Alert sells its own relay (Model RM4) but it is twice as expensive. Because Kidde and First Alert (and I believe all others) send the “smoke/fire” signal over the interconnected line as a straight 9V signal, either should work (or you could roll your own for even cheaper).

The problem comes with the CO signal. Each brand apparently uses its own form of pulse signaling over the same interconnect wire to signal a CO alarm in a way that is not detected as a “fire/smoke” signal.

Kidde sells a second CO alarm relay harness that will trigger only if a CO signal is present. Kidde’s protocol is patented so I assume First Alert/BRK does not use it and therefore the Kidde CO relay will not work for me: https://patents.google.com/patent/US6791453B1/en

I am not sure if the First Alert relay distinguishes between a fire/smoke alarm and a CO alarm or if it triggers on both. The manual suggests both, which would make sense because First Alert does not sell a second CO only relay. I assume the Kidde Relay will only respond to fire/smoke alarm signals sent by First Alert, but there is a possibility the different CO protocol could trip both.

GOAL
I’d like to isolate the fire/smoke alarm signals sent to HA from CO signals since each commands an entirely different response. I’m fine removing the Combo detectors and keeping the interconnected alarms Smoke/Fire only. (In fact, I think I’d prefer it, because having all the smoke detectors go off for a CO alarm is confusing).

Ideally, I could have a separate relay/trigger for each detector so I can distinguish between a basement CO event or first floor, etc.

POSSIBLE SOLUTIONS

  • Keep the Combo CO detectors on the same interconnected circuit and try to figure out the First Alert CO signal and roll my own relay.

  • Remove the Combo CO detectors from the interconnected circuit and switch to all wireless zwave detectors. Is Fibaro the only option?

  • I’ve found some hardwire CO detectors with built in relays, but I don’t really want to run new wiring. Are there any battery powered detectors with relays?

  • Use plug in/battery CO detectors and then use a zwave audio sensor to detect the audio alarm (e.g. the Ecolink audio detector). This would allow each alarm to be separately detected, but I don’t trust this kind of linking. If I went that route, perhaps it would be cheaper to use an M5Stack Echo and just listen for the alarm that way?

  • Ideal Solution: a plug-in CO detector with a relay or a way to ‘add’ a relay.

I assume others have gone through this before?

I was planning something similar but I decided to go with a ‘listener’ device.
I just replace 3 of my Nest Protects with First Alarm hardwired/interconnected smoke/CO detectors. I bought my NEST products before Google gutted them. They just got to their 10 year end of life.
For the listener I went with the:
“Ecolink Zwave Plus Wireless Audio Detector Wireless Audio Detector for existing Smoke/CO sensors, White (FF-ZWAVE5-ECO)”
https://www.amazon.com/gp/product/B071Z8NM8N/ref=ppx_od_dt_b_asin_title_s02?ie=UTF8&psc=1

I also was looking at the relay but then I would have also had to get something else like a Z-wave dry contact sensor to relay to Home Assistant, so I went with the Ecolink. I will say that what you might initially think is the learn button is not; the learn button is hidden inside and is small; there is another bigger and prominent button…that’s not the learn button that is the ‘tamper’ button.

I have upgraded my 10+ years old smoke detectors with Kidde Smoke + CO combo hard wired units, they are interconnected. Bought Kidde smoke and CO relays and connected them to my DSC security system on individual zones to report on HA but not to trigger alarm.