First Alert Hardwire Smoke Alarm | SMI100-AC, 9V Battery Backup

I got this as a replacement for an older hardwired smoke alarm, and it was pretty straightforward to swap in. The included quick connect plug made the setup easier, and it fit nicely once mounted. I also like that it has battery backup, so it still gives some peace of mind during a power outage. One thing I appreciated is that it is made to reduce nuisance alarms from normal cooking smoke, which is honestly a big deal if your old detector was too sensitive. The test/silence button is easy to reach, and the alarm feels solid, not flimsy or cheap. It also has the interconnect feature, so compatible alarms in the house can sound together. This is not a fancy smart unit, but for a dependable hardwired smoke alarm, it does the job well. Price felt fair, install was easy, and overall it seems like a solid upgrade from older builder-grade detectors.

I was able to replace 7 old Firex smoke detectors with these using an adapter. I had to buy the adapters separately on Amazon. These were very easy to replace. I just unscrewed the old screws (not all the way, just enough to take off old base plate). These base plates fit perfect on the existing screws, so just tighten then down. I attached the adapters to the existing wires and then to the new smoke detector, screwed the new detector onto base plate, pulled out battery pull tab, tested and good to go. I bought 12 detectors in June 2026 and they were all manufactured on May 15, 2026 so I had no issue with any being years old as others have said. All detectors tested good (loud alarm, interconnected with no issue) and have had no false alarms. Overall great purchase!

Upgrading our home’s smoke alarms to this 3-pack was a smooth and worthwhile improvement. From start to finish, the process was much easier than I expected. Installation was straightforward, especially if you’re replacing existing hardwired units. The wiring harness connected cleanly, and the mounting brackets lined up without any hassle. Once installed, setup was quick—everything synced as expected with the interconnect feature, so when one alarm is triggered, they all sound. That added level of coverage brings real peace of mind. The battery backup is another big plus. It’s reassuring to know the alarms will still function during a power outage without needing to think about it. The access for the battery compartment is simple and user-friendly, which makes future maintenance easier. I also appreciate the clean, low-profile design. It blends into the ceiling without drawing attention, but still feels solid and well-built. The test/reset button is easy to access, and the alarm itself is loud and clear—exactly what you want in an emergency. Overall, this set delivers on reliability, ease of installation, and essential safety features. If you’re looking to replace older hardwired alarms or upgrade to a system with interconnect capability, this is a practical and dependable choice that doesn’t overcomplicate the process.

Simple, adaptable, effective. Needing to bring my dwelling up to code, I bought this and found that the manufacturer had prepared both for new construction (with house current) and old construction (battery only). I hadn't known, but whether I did or didn't, the vendor had prepared for either way. The item itself was easy to install - I had my adult daughter install her own in her part of the house, and she is not accustomed to doing this kind of thing for herself.

Written after approx 1 year of use. Great product, and easy to install. This was a replacement for units that were originally installed in my house. They fit perfectly into the existing mounts and have been working like a charm.

I bought several of these to replace decade-old Kidde smoke alarms. As far as I can tell, Amazon in the US market sells only three major brand options: Kidde (Firex), Siterwell, and First Alert. (Some outlets like Home Depot appear to sell other brands like Universal.) I bought these First Alert alarms for my apartment rental because they are fairly cheap but still get pretty high customer ratings for no-fuss dependability. I don't need or want expensive fancy alarms that I can hook up to my home internet or for which I had to create yet another corporate account, especially since I already have home security cameras. I didn't want to shell out a lot of money for a 10-year sealed battery because I don't know if I'll be staying in my rental that long. I did want fire alarms that met my city laws for rentals: hardwired with a battery backup, uses 9-volt batteries (because I had bought a bunch for the Kidde alarms), and interconnected (so that if a fire erupts in one area of my home, the rest of my home can be alerted as quickly as possible). Well, these First Alert alarms meet all those criteria. Installation was fine and easy, even though that was the first time I've dealt with wire nuts and figuring out my home's internal wiring. (Make sure to turn off your electricity at the circuit box!) Also, I used a permanent marker to mark how the + and - ends of the 9V battery should be put in, because you can't really see the plastic casing's markings. These alarms work fine. I don't do a whole lot of cooking on the stove, so I am also less concerned about false alarms. No issues so far in the past few days since installation, except for one problem. I am taking one star off because this alarm's always-on green LED light is insanely bright and impossible to dim with coverings on the outer casing alone (without defeating the alarm's operation). It's fine during the day, but at night in a bedroom, the piercing neon green light is so obnoxiously bright that it bothers me in my sleep. This LED light problem is apparently endemic to all smoke alarms, including all three major brands I listed, and I understand why this light cannot be turned off. However, these First Alert alarms have the additional feature that even if you cover the plastic casing's pinhole for the green light with electrical tape, the green light will leak out underneath and through all the other gaps -- which must remain open and uncovered (because that's how the alarm works, by detecting the smoke that reaches inside through the gaps). If that was some kind of a security feature, well it backfired because it forced me to take apart the plastic casing and put the black electrical tape directly over the green LED light bulb on the printed circuit board. (This is labeled "LED2" on the motherboard, while the red light is labeled "LED1".) Although you're not supposed to pry open the plastic casing to access the internal parts, doing this doesn't disrupt or damage the motherboard, so it went fine for me. However, I deliberately did not do a complete job of covering the green LED; I left the tape a little loose so that some light will leak out. You can see the result in the final photo -- you can still see a green light, but it is very faint in the dark. In total darkness, I can definitely see a green globe of light emanating from the alarm, but the brightness is tamped down enough that I can ignore it in my sleep. (It is so faint that it was impossible for me to take a photo of it with my smartphone.) So, overall, these First Alert smoke alarms seem like good, simple basic alarms for most areas of your home, but be aware that in a bedroom, the LED light could disrupt your sleep if left uncovered.

Dependable home safety and peace of mind. The hardwired interconnect feature is especially valuable because it helps ensure all connected alarms sound together, while the battery backup adds extra reassurance during power outages. It feels like a practical, reliable option for protecting your home, and the installation-friendly design makes it even more appealing. Overall, it’s a smart purchase that combines safety, convenience, and solid value.

The fit perfect . Perfect replacement. My 10 year ones were all going off one at a time, some in the middle of the middle of the night. Hardwired , came with battery. Was not hard to changed out. Just made sure I cut out the power. Removed my old ones and replaced. Didn't need to adjust anything. The little light don't seem too bright at night . Bought 9 total .

Works with previous wiring and brackets from older First Alert or BRK devices. Very simple. Works great.

This hardwire smoke alarm was a snip to install. The screw holes in the mounting plate lined up perfectly with the electrical box in the ceiling. The alarm tested well. Looks good also.

Muy buenos, sólo que tiene un chiflido que indica que la batería está baja o algo así es que antes de instalarlos recuerda remover la película que deja que la batería haga contacto

Easy to replace the Kidde. Looks new and modern and is very easy to install especially if you're familiar with wire nuts and have some at home. If not, they're cheap at your hardware store. Use orange color wire nuts for the wires leading to the smoke alarm. Watch YouTube video on how they work. Very simple.

Easy to install, connected with non First Alert alarms immediately. Installed a month ago and no problems, so far.