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Extended holiday returns
FREE refund/replacement until Jan 31, 2027 Learn more
FREE refund/replacement until Jan 31, 2027 Learn more
This item's return window has been extended for the holiday season: FREE refund/replacement until Jan 31, 2027
To qualify for a full refund, items must be returned in their original, unused condition. If an item is returned in a used, damaged, or materially different state, you may be granted a partial refund.
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Availability:
In Stock.
Arrives
Wednesday, Nov 18
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At a glance
- Condition
- New
- Size
- 1-Pack
- Style
- Precision Detection
- Pattern
- SMI100-AC
- Dimensions
- 5.6"D x 5.6"W x 1"H
- Weight
- 9.6 oz
- Color
- White
Features 6
- First Alert's Precision Detection advanced sensing technology complies with new industry standards to reduce cooking nuisance alarms and provides early warning in the event of a home fire emergency.
- Through early warning interconnect, when one alarm sounds, all compatible alarms will sound
- Battery backup provides continuous protection during power outages
- Alarm indicator visually identifies the unit that initiated the alarm
- Quick Connect Plug included allows for easy installation with no need to rewire
- The date shown on the product is the Manufacture Date, which identifies when the product was produced
Description
The First Alert SMI100-AC Hardwire Interconnect Smoke Alarm with Battery Backup meets new industry standards utilizing First Alert's Precision Detection advance sensing technology. This hardwire smoke alarm is easy to install and replace existing alarms with no need to rewire. Plus interconnect compatible alarms to create a whole home alarm system to help provide an early warning.
Specs 19
| Brand | First Alert |
|---|---|
| Style | Precision Detection |
| Power Source | Corded Electric |
| Color | White |
| Product Dimensions | 5.6"D x 5.6"W x 1"H |
| Item Weight | 9.6 ounces |
| Alarm | Smoke Alarm |
| Sensor Type | Ionization |
| Unit Count | 1 Count |
| Model Number | SMI100-AC |
| Number of Items | 1 |
| Item Highlight | SMI100-AC, 9V Battery Backup, 1-Pack |
| Manufacturer | Resideo |
| UPC | 029054022462 |
| Built-In Media | Easy Adapter Plug, 9V Alkaline Battery |
| Item Type Name | Smoke Alarm |
| Mfr Part Number | SMI100-AC |
| Product Style | Precision Detection |
| Item Dimensions D x W x H | 5.6"D x 5.6"W x 1"H |
No specs match.
Frequently asked questions
If you place your order now, the estimated arrival date for this product is:
Wednesday, Nov 18
Yes, absolutely! This item's return window has been extended for the holiday season: FREE refund/replacement until Jan 31, 2027.
To initiate a return, please visit our Returns Center.
View our full returns policy here.
To initiate a return, please visit our Returns Center.
View our full returns policy here.
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Top Amazon Reviews
Great Smoke Detectors
Size: 12-Pack
Style: Precision Detection
Pattern Name: SMI100-AC
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!
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Reviewed in the United States on July 5, 2026 by Joseph Clark
Peace of mind and reliable
Size: 3-Pack
Style: Precision Detection
Pattern Name: SMI100-AC
This First Alert SMI100 smoke detector is easy to install with the included mounting bracket. Minimal false alarms from normal kitchen cooking or steam.Loud alarm that can easily be heard from any bedroom. What I appreciate most is the reliability. My old detector would go off every time I opened the oven, but this First Alert model has remained quiet during normal cooking while still passing weekly manual tests. The test button is easy to reach, and the 85-decibel siren is incredibly loud—definitely enough to wake up the whole house in an emergency. It gives my family great peace of mind. I highly recommend it to anyone looking for an affordable, reliable upgrade to their home safety.
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Reviewed in the United States on July 18, 2026 by Fatina Williard
Good replacement alarm with simple install and battery backup
Size: 1-Pack
Style: Precision Detection
Pattern Name: SMI100-AC
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.
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Reviewed in the United States on April 2, 2026 by Yifan jin
Easy replacement.
Size: 1-Pack
Style: Precision Detection
Pattern Name: SMI100-AC
My old smoke alarm was constantly beeping/chirping. Changed the battery & no change. Read online that a smoke alarm generally lasts 10 years & that's when this one was installed. This replacement was perfect. Just twisted the old one off. Reconnected the wire plug, twisted the new one on & voila...no more chirping. Cheaper than Lowes too.
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Reviewed in the United States on October 1, 2026 by Leann
Easy Install and Setup
Size: 3-Pack
Style: Precision Detection
Pattern Name: SMI100-AC
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.
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Reviewed in the United States on March 25, 2026 by Hannah
Good smoke alarm, but always-on green light is too obnoxiously bright for the bedroom
Size: 1-Pack
Style: Precision Detection
Pattern Name: SMI100-AC
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.
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Reviewed in the United States on July 10, 2026 by customer
Great
Size: 1-Pack
Style: Precision Detection
Pattern Name: SMI100-AC
Worked fine. Easy to install. Used to replace a bad smoke alarm.
Reviewed in the United States on September 28, 2026 by Terry Lynn
Device has unlimited lifetime
Size: 1-Pack
Style: Precision Detection
Pattern Name: SMI100-AC
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.
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Reviewed in the United States on September 3, 2026 by Harold D.