First Alert SMI100-AC, Hardwire Interconnect Smoke Alarm with Battery Backup, 1-Pack

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!

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 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.

Well-made device that was also easy to install. Unlike the Kidde alarms, this device has unlimited life without requiring to be replaced every 10 years. However, the wire leads are very small and the purchaser should have 2 small wire nuts that work with fine wires. I had some that were used for a model railroad.

Installed right out of the box. Fit right into the existing bases. Comes with bases and plug replacement but you dont need them if yours are undamaged. Highly recommend.