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

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.

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.

Works as exactly as described. Easy to install. Wild buy again.

This smoke detector has the same great features and does the job it was intended for, and half the price as my other model previously installed by the builder.

Great after a quick install and first day. Had to replace two very aged and non working sets from 1998, so wiring harness naturally did not fit. Swapping out the new harness is predictably simple. New mount fit nicely against the ceiling and new unit locked into place.

This is a perfect replacement for First Alert model 9120BFF. The new model # is SMI100-AC.Good product , fair pricing.

Very easy to install over my old model (BRK 4120b). I could've even left the same wall base in, but it had become discolored over the years so I went ahead and replaced that with the one provided, too. I'll come back and edit this if there's a problem but they passed testing when first installed, the light is still there inside if you look, and it still passes testing a month later. We test ours every New Years so if it goes bad in a few short years I'll update this.

Replaced 20 year-old one with this one works well