Combination Smoke & Carbon Monoxide Alarm, Interconnect Hardwire Detector with Battery Backup, SMICO100-AC, 1-Pack

I have been a master electrician for 32+ years. If you're not 100% sure of what you're doing, hire a professional! Ok a lot of people are complaining about the new connector. It literally takes 60 seconds to rewire. I rewire anyways so I can put a meter on the ceiling wires to make sure everything is as it should be. The base is a tad smaller than my previous ones. They were from a different company though. It presented zero issues during the installation. I have 3 detectors upstairs and one in the basement. I wired them all and they all worked inline perfectly. When one goes off, they all go off. The alarm is very loud and high pitched. It also tests both the smoke and CO² detectors when pushing the test button. You'll get a beep and then another beep. Then it repeats. Meaning they are all working. Bonus each detector comes with a pre installed Duracell 9 volt battery. You also receive a dust cover for the detector if you need to work in that room. Kicking up dust or debris can get inside the unit and fault it. Nice little freebie to have. Although I didn't need, they come with very detailed instructions with diagrams. After I installed them all I tested it my way using certain techniques to get both detectors to alert. They passed on both smoke and CO². For this price point, I am very happy with these units. It gives me a sense of security knowing my family is protected. Please mark the back of your detectors with the date you install them. I use a black marker. Also be sure you were shipped the correct units. It should say on the outside label Combination Smoke/Carbon Monoxide Alarm. I've posted pictures along with a video. I hope this aids with your decision whether these are for your home or not. I will update again if I have any issues in the future. As of now they are working as they should and I again, am very happy with my purchase.

We recently installed the First Alert Combination Smoke & Carbon Monoxide Alarm, Interconnect Hardwire Detector, and we are extremely pleased with the decision. This unit is an outstanding choice for anyone looking to upgrade their home safety system, combining two essential protections into one convenient device. Top Features We Appreciated Dual Protection for Ultimate Peace of Mind: The biggest win here is having both smoke and carbon monoxide (CO) monitoring in a single unit. It gives great peace of mind knowing that the home is covered for two of the most critical household threats. It simplifies maintenance and ensures comprehensive safety. Seamless System Integration: A major selling point for us was its compatibility with our existing setup. This First Alert detector fit perfectly into our previous interconnected system (hardwired). The installation was straightforward, and it immediately linked up with the other alarms in the house, ensuring that if one goes off, they all do. This interconnectivity is vital for alerting everyone, no matter where they are in the house. Reliable Brand: First Alert is a name synonymous with home safety, and the quality of the unit feels robust and reliable. Conclusion If you are looking to replace old, separate smoke and CO alarms, or if you simply need to upgrade to a hardwired, interconnected system, this combination alarm is a superb choice. It delivers on its promise of simplifying safety while maximizing protection. Highly recommended!

I recently installed the First Alert Combination Smoke & Carbon Monoxide Alarm (SMICO100-AC), and I’m very pleased with its performance. Installation was straightforward — the hardwired setup with battery backup provides peace of mind knowing it stays powered even if the electricity goes out. This alarm detects both smoke and carbon monoxide, which gives me confidence that my home is protected on multiple levels with just one device. It’s loud and responsive during testing, and the included battery backup is a great safety feature. The interconnect capability is excellent too — when one alarm sounds, all interconnected units activate, which is ideal for larger homes. Overall, this feels like a high-quality product from a trusted brand. Easy to install, dependable, and a smart investment in home safety. Highly recommend!

While First Alert lists SMICO100-AC as direct replacement for the discontinued 9120B, it is NOT the same size and will NOT fit existing 9120B mounting rings. While they appear to be the same, the newer model is (strangely) a fraction of an inch larger around. Changing mounting rings is easy, but will be required. The new mounting rings are larger inner diameter, smaller outer diameter, so will not cover ceiling covered by the older mount. Plug is compatible and units appear to work as advertised. This would easily have been 5 star, I have NO idea why they didn't make the mounting match!

Replaced an SC9120B with this new model. Overall install took about 10 minutes. As others have said, you cannot reuse the bracket from the SC9120B as this new one is slightly smaller around. HOWEVER, the mounting screw positions do match up perfectly so it's really a minor issue. Just back the screws out a couple turns to be able to remove the old bracket and then pop the new one on. The wire harness that was used with SC9120B is also the same on this newer model, so you wont need to replace the existing one with the new wire harness that was included.

Easy to install to replace old smoke alarms that were installed in 2013. I didnt have rewire anything. Just popped the old one off and popped the new ones in.

Perfect replacement for all my FA smoke detectors in home. Easy to install directly in the same installed mounting plates.

I recently purchased four units. Two of the SMICO100-AC type and two very similar units without CO detection capability. This review applies to both types. The detector has a green LED to indicate that it is connected to 120V. Unfortunately, the light is far away from the observation hole, so it is very difficult to see. In fact, I could not see the light through the observation hole. Only in the space between the test button and the body of the unit. Although there should be no need to install the battery when the detector is first installed, replacing the battery is very, very tricky. Especially after the unit is mounted. Attempt to find the straight side of the drawer that opens up from the unit and align the long edge of the battery with that side. Also pay attention to the position of the positive terminal when removing the old battery. I may have missed it but I did not see a marking for the position of the positive or negative terminals. I could not easily read the user manual even with strong reading glasses. The font is just too tiny. Fortunately, the manufacturer has placed a manual on the web. The manufacturer has both zeros and "O"s in its model number. So I had to make a couple of searches to find the manual. The red wire to interconnect the detector with other detectors is capped. It is necessary to use a wire stripper or equivalent to remove the "cap." The manual does not mention this. The supplied connector with wires is difficult to plug in and very difficult to unplug. I had better luck putting the connector on the unit before I finally installed the unit using wire nuts to connect to the house wire. The wire nut connection to the first wire connected held the unit while I installed the remaining two wires. All in all, it would have been better for me to just get rid of the connector. All the units worked OK after installation. I have had problems with all the smoke detectors I have used or installed. The issues with this unit are comparable with other units I have had. I have my circuit breaker box marked to identify the breakers to turn off the units. This is helpful when the battery goes bad in the middle of the night and the unit starts chirping. It is also necessary on my previous units to take out the depleted battery. An update on 12/7/2025: About 1 year and 3 months after the installation a battery died in one of the units I installed. The unit woke me up at 5:00 AM. I think getting on a step ladder and replacing the battery is a slight risk that I do not want to undertake nine or so times during the 10 year life of the smoke detector. (I am 81 years old) So I will purchase a similar unit with a 10 year battery. I have read in some reviews that Amazon does not take returns on smoke detectors. Not sure it is true; but I will none the less purchase the smoke detector from Lowes . . . but then I do not know that they will take the return either as it seems to be a First Alert policy to not take returns. For those of us with sleep issues, the battery failure in the cold dark night is a little bit of a health issue. So I wish the organization that provides the specs for these units would require more than just fire and smoke considerations. Or maybe all the units should be required to have 10 year batteries. Less falls off ladders and less sleep related health issues.