First Alert 9120BFF/ SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, White, 1-Pack

It took me a long time to decide which smoke detectors to buy for my house, this model or the brand made by Kiddie. My house already had the Kiddie brand and this would mean a much faster replacement for all the smoke detectors in my house. Over time the Kiddie brand tended to chirp a lot and that drove everyone in the house crazy, especially my older and wonderful dog. My daughter said a candle lit in her room also set off all the smoke detectors in our house. If you go to the store you will find these labeled "BRK" with the words "First Alert" in smaller letters underneath and they come in a yellow and black box. It is unfortunate. Yellow and black packaging reminds me of generic food items back in the 70's and these items had a reputation for being below par. If I did not know what I was looking for I would have passed over these units in favor of something else, and I also noticed that BRK and First Alert puts their more expensive models in fancy and beautiful packaging. Thus, I fear that this company intentionally brands this "entry level" smoke detector in yellow and black to dissuade people from buying it and moving up to the more expensive models. I bought the contractor pack of this item as well as three single units to replace the nine smoke detectors in my house. All of these come with a free battery. I knew I would have to take down the old detectors, take down the mounts, and disconnect the old wiring in order that I be able to put in the new mounts and the new wiring for this smoke detector. It is a job that takes about 10 minutes at the most to completely swap out each of the units. Remember to shut off the circuit breaker! The alarm itself looks great. I like the design a lot better than the flat plastic orb. Once the new wiring harness is connected and the mount is secured to the ceiling, the new detectors snap easily into place for the wiring and you twist it onto the mount. The battery compartment is on the side and although the door for the battery looks cheap, all held up well and none broke. The alarm itself is easy to test, push the big button, and the alarm is loud enough to get anyone's attention. So far, cross our fingers, there have been no errant cheeps and no false alarms. Now to give Kiddie credit our old alarms were nearing the end of their expected lifespan so the new ones would have probably worked as well. I admit it, I went for the name brand!

I got this to replace a smoke detector, which was acting up and this worked perfect. The price was great. Installation was easy. Connected simply. Works great. Matches the one I was replacing. Piece of cake! Noise/alarm is loud. Peace of mind is back. Pleased w this replacement.

I only had one little hiccup and overall I am quite satisfied with these detectors. It was quite easy to replace my old detectors with them. They mount on the base plate in a nice easy fashion and the batteries are very easy to replace. Much easier than in my old ones. The one hiccup? I replaced my old ones because they started to go off randomly and replacing the batteries didn't fix it so I concluded that they had simply gotten too old. Then when I replaced them with these new ones ... they still went off randomly. But this time replacing the batteries fixed the problem like it normally does. So don't rely on the batteries that these things are shipped with. Definitely a small issue.

I replaced all of my smoke alarms after coming home from vacation to find two of the old ones beeping. I decided to order all new ones for my house since they were over 12 years old. They were easy to install and only took a short time to do all five. This was in October of 2025, and in April 2026 we woke up to a beeping smoke alarm in our bedroom, it had only been about 6 months since they were installed. I am fairly satisfied with the First Alert Smoke Detectors I purchased, I am just dissatisfied with the fact that the battery in this one failed so soon. Now I am wondering if others will fail soon. I might suggest replacing the battery that comes with the detector be replaced by new ones, but you would expect that new smoke detectors would have fresh batteries so to last longer than 6 months.

Excellent Smoke detectors. Work well. Reliable. Dependable.

I researched various brands of smoke detectors and decided based on reviews and other factors (UL ratings) that the First Alert / BRK brand was the best and most reliable. I also read about ionization vs photoelectric sensors, and that many different websites recommend having a smoke detector that has both types of sensors installed in a single unit to alert to both types of common house fires (smoldering vs rapid flame combustion). I found the First Alert model smoke detector with both ionization and photoelectric sensors would not work in my application, as the combination sensor smoke detector is battery powered only. The smoke detector configuration in my home is hard wired. So I decided to purchase the First Alert Model SMI 100-AC, which has the ionization type sensor only, and is equipped to be hard wired and has 9 volt battery backup. The smoke detectors I was replacing were USI brand and the old pigtail was not compatible with the First Alert brand. So all 7 of my smoke detectors needed the new hire wire pigtail installed that comes with the First Alert detector. I found this job to be very easy and instructions for installation were very straightforward. Took me a total of about 2.5 hours to rewire all pigtails and install all 7 new detectors. I tested each new detector individually as each was installed, and then again as an interconnected series across the complete circuit. All worked perfectly and all are showing solid green LED, which indicates they are all receiving AC power and alarm and battery backup are working and active. The green LED light is very subtle and does not cast any light at all in a dark room that would be considered bothersome or glaring. Very happy with my choice and I highly recommend to anyone needing to install new smoke detectors or replace old ones that have reached end of life like mine.

Great replacement for old First Alert 9120 db smoke detector.

Replaced one upstairs works great