Inspired by
this post. I decided to replicate this. Most of the details are already there. I used an
Ecolink Door sensor and the Kidde SM120X relay. SM120X works for smoke alarms and you need another CO120X for CO alarm.
I wired the relay into the contact sensor's external switch and now the sensor changes status whenever the interconnect is triggered. I checked with the other alarms in the house and if anyone of them triggers, the door sensor changes status and therefore notifies me.
I have about 10 smoke detectors in my house, so for about $45 bucks (all inclusive), this is not a bad alternative to Z-wave smoke alarms which AFAIK are not available in hardwired versions.
Now, if only there was a way to change the icons in the app :-)