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!

Easy to install. Works great so far.

Received this quickly. It replaced my First Alert and was easy to install since it was the same size and I used the same mount to hold it in place. Came with the 9 volt battery back up. Tested it and we are good for another 10 years.

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.

Works great! No issues.

easy install works great good price

I needed to replace a First Alert model 9120B: it started to chirp because the battery was low. When I removed it from the ceiling I saw that it was over ten years old. I read that smoke detectors should be replaced at that age. I wanted an identical replacement so it would fit on the same mounting bracket in my ceiling and use the same power connector that's connected to AC power in the ceiling. I saw this model, 9120BFF, and the photos on the Amazon page show the unit labelled 9120B despite the "FF" at the end of the model number in the product description. I wasn't sure if it was the same, so I tried searching for model 9120BFF, but all I found was the same page on Amazon. But I ordered it anyway, and it is indeed the First Alert model 9120B. It is an exact replacement and works great. It fits on the same mounting bracket and uses the same power connector that my old smoke detector used. It comes with a new mounting bracket and power connector, which I don't need. And it comes with a new 9V battery: there's a plastic tab covering the battery terminals so no power is drawn until you pull the tab out of the unit when you install it. So why is this called model 9120BFF instead of 9120B? I think it's the packaging: see the picture attached. It comes in a plain corrugated box, which I assume is how they sell it to contractors. It's not in consumer packaging with a glossy cover like you'd find in a retail hardware store. But it's the same product: the label on the unit says Model 9120B, and it comes with instructions for that model. There's one other clue that it is sold to contractors: it includes a plastic dust cover that looks like a miniature shower cap. The dust cover is to be used during construction to keep dust out of the unit; you remove it when construction is finished. (It could be that the dust cover is also in the consumer version; I'm just guessing here.) Anyway, I'm happy with the purchase: it didn't require any ceiling work to replace my old smoke detector, which was my goal.

Installed to replace old Universal Security Instruments networked hardwired smoke alarms, which had reached their end of life. Installation was simple using the existing wiring, tested fine, and seem to be working well. Haven't tested with actual smoke. Replaced with First Alert devices because USI has no phone customer service support and is now owned and made by Feit in China. The First Alert devices had the highest ratings with almost no 1 star ratings, and do provide responsive phone customer service support.

We bought this to replace our expired smoke detector. It was easy to install and it fit the base that was already mounted on our ceiling. This avoided removing a base and damaging paint, just to install a new base.

Works good so far :)

Wired up easy work perfect

Good but the new battery that came with it was dead. Almost returned it thinking something wrong with the unit itself

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