In 2020, I remodeled my vintage bungalow in 1967 and, as part of that remodel, made the decision to invest in as many new technologies as it made sense to do. Part of this investment was smoke and CO2 detectors. I bought six Onelink First Alert smoke detectors and carbon monoxide detectors, model no. 1042136. They checked a few boxes for me when I tried to decide what to receive. * Battery powered - My old house was not required to have a cable smoke detection system when it was built and I did not want to have an electrician run a new pipe (needed where I live) and wiring. * Interconnected - It is even said in advertising that when one goes out, everyone goes out. No chance of sleeping through an alarm in the basement when I'm upstairs. * HomeKit compatible - This is the goal. Everything in Homekit (native where possible) and receive alerts about the potential danger wherever I am. At the end of my refurbishment, in September 2020, I bought six of these detectors, three on the main floor and three in the basement. The initial set-up of these things was a huge pain. I went through the configuration several times, because the devices looked "unanswered" in HomeKit, and in the OneLink app they showed "required setting". I opened a support note and they asked me to remove and add the devices again and say I could see them connected and checking out of their systems. However, they confirmed that the problem was prevalent among customers using iOS 14.2. The First Alert called someone to guide me through the setup and make sure I had no other problems. It was a pleasant touch at the end and I appreciated the call. After the next iOS update and a few updates to the Onelink app, the devices were stable and without connectivity issues. The interconnect function does not work reliably. That is, about the 6 alarms that we have installed in the house, it is a game of chance when other additional alarms are triggered. I had only one CO2 alert last year, due to a leak in my basement space / workshop, no matter what you want to call it. The only alarm that went off was the direct one in that space. None of the other alarms in the house were triggered. Other examples in this regard are detailed below. False alarms happen out of nowhere. A few weeks ago (23.06.2021) my alarm in the living room triggered a fire alert around 21:00 one evening. After we silenced her, the rest of the evening was quiet until about 2 in the morning, we were brought back to reality by the same device that warned us of a non-existent fire. The interconnection triggered I think four of the six total alarms in the house. A quick email to First Alert support with details about the problem gave me a return shipping label for the faulty alarm and a confirmation that a new one was on the way. Early in the morning (07/06/2021 at 03:49) the device in my dining room alerted us to a fire in which there was none. That device and one in three in the basement were the only devices triggered. I sent support via email today, I expect to be sent a new device again. As for the software, I don't like much on both the Onelink and the iOS side. Let's start with the silence of the alarms. You can only do this from the software in the Onelink application. There's no way to reduce device mute in HomeKit, so you're actually addicted to the Onelink app or you can physically go to your device (more on that in a bit). The Onelink application does not send critical alerts in iOS, it depends on you or not, but you only know if your phone is in DND mode you will not be alerted by alarms. In the Onelink application, each device has a log for recent activity. I don't know what is considered "recent", but there is no record of activity on any of my devices in the last few weeks, despite the two false alarms. When working, disabling alarms can only be done via the Onelink application or by physically pressing a button on the device. I had various experiences with this. In the case of the false CO2 alarm, the move through the application did not work. I had to go to the device and hold down the Silent button. The false alarm of 23.06.2021 triggered four devices, and the software reduced to alarm the device that initiated the alert. The others were not displayed as triggered in the application and had to be silenced manually. This morning, I didn't even bother with the app and jumped out of bed and held the button on the only device upstairs that was alarming and then went down to silence the only other device triggered. I hope you enjoyed reading all this and I hope my experience has been enough to help you decide whether or not these devices are something you want in your home.