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First Alert

First Alert BRK 3120B Hardwired Photoelectric and Ionization Smoke Alarm with Battery Backup, Dual Sensing Smoke Alarm, 1-Pack

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Style: Standard Detection


Size: 1-Pack


Configuration: 10-Year Battery


Features

  • The front cover design of the alarm may vary but product function remains the same.
  • The First Alert Hardwired Dual Sensor Photoelectric and Ionization Smoke Alarm with Battery Backup is designed to help provide peace of mind.
  • This dual sensor, photoelectric and ionization alarm alerts you to both smoldering and fast-flaming fires in the event of a home fire emergency.
  • Hardwire alarm includes battery backup for protection during power outages.
  • Two latching features help indicate a low battery or the originating alarm in a system.
  • A single test button makes alarm easy to test regularly.

Description

The First Alert Model No. 3120B is a wire in, 120V AC 60Hz single and/or multiple station photoelectric and ionization dual sensor smoke alarm specifically designed for residential and institutional applications including sleeping rooms of hospitals, hotels, motels, dormitories and other multifamily dwellings as defined in standard NFPA 101. Model 3120B complies with UL217, CSFM, NFPA 72, HUD, FHA and other agencies that model their codes after the above agencies. It meets building codes where AC/DC photoelectric and ionization combination smoke alarms are required. The BRK 3120B is a state of the art hardwired with battery backup smoke alarm that features dual photoelectric and ionization smoke sensing technologies. This alarm features two latching features and two silence features. Alarm Latch: Easily identifies initiating alarm even after alarm condition has subsided. Low Battery Latch: Identifies which unit is in low battery condition by blinking the green power light. Low Battery Silence: Temporarily silence the low battery chirp for up to eight hours. Alarm Silence: Silence alarm for several minutes. Other features include an85dB horn, single button test/silence, an easy access battery drawer and dust cover. OptiPath 360 Technology: Exclusive patented technology provides 360 degrees of direct access to the smoke sensor. Two locking features are provided to prevent battery theft and/or theft of the unit. Connection to AC power is made with a Quick Connect wiring harness. Installation is quick, easy and cost effective.

Brand: First Alert


Style: Standard Detection


Power Source: Battery Powered


Color: Dual Sensing Smoke Alarm


Product Dimensions: 2"D x 5.25"W x 5"H


Item Weight: 11.68 ounces


Alarm: Audible


Compatible Devices: photoelectric


Upper Temperature Rating: 38 Degrees Celsius


Sensor Type: Photoelectric


Brand: ‎First Alert


Style: ‎Standard Detection


Power Source: ‎Battery Powered


Color: ‎Dual Sensing Smoke Alarm


Product Dimensions: ‎2"D x 5.25"W x 5"H


Item Weight: ‎11.68 ounces


Alarm: ‎Audible


Compatible Devices: ‎photoelectric


Upper Temperature Rating: ‎38 Degrees Celsius


Sensor Type: ‎Photoelectric


Global Trade Identification Number: ‎34


Number of Items: ‎1


Manufacturer: ‎First Alert


UPC: ‎029054015334


Part Number: ‎3120FF


Item Weight: ‎11.7 ounces


Item model number: ‎3120FF


Batteries: ‎2 AA batteries required. (included)


Is Discontinued By Manufacturer: ‎No


Size: ‎1-Pack


Pattern: ‎1st Generation


Item Package Quantity: ‎1


Included Components: ‎Smoke Detector, batteries, mount, user's manual


Batteries Included?: ‎Yes


Batteries Required?: ‎Yes


Battery Cell Type: ‎Alkaline


Warranty Description: ‎10 Year Limited


Date First Available: October 3, 2014


Frequently asked questions

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This item is non-returnable:

Non-returnable. Transportation of this item is subject to hazardous materials regulation

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Top Amazon Reviews

    • Reliable Smoke Protection Without the Hassle of Battery Changes
Style: Standard Detection Size: 1-Pack Configuration: 10-Year Battery
Reliable Smoke Protection Without the Hassle of Battery Changes I’ve been gradually upgrading the smoke alarms in my home, and this First Alert SM310 has been one of the easiest and most reassuring additions. The 10-year sealed lithium battery is a huge selling point—no more late-night chirping or running out for 9V batteries. Once mounted, it’s basically set-and-forget until replacement time. What I really appreciate is the dual-sensor design. It combines photoelectric and ionization sensors, which means it’s better equipped to detect both fast-flaming and smoldering fires. That gives me more peace of mind, especially with kids in the house and multiple floors to cover. The test/silence button is also handy—easy to reach, and it worked perfectly during my trial run. Installation was quick with the included hardware, and the alarm sits low-profile against the ceiling without looking bulky. The sound output is loud enough to be jarring (as it should be), easily heard through closed doors. If I had to nitpick, I’d say it’s not interconnected, so it won’t set off other alarms in the house if one goes off. For some setups, that’s an important feature to consider. But for standalone coverage—especially in bedrooms, hallways, and smaller homes—it’s an excellent choice. Bottom line: A dependable, no-maintenance smoke alarm with dual sensors and a 10-year battery that delivers both convenience and safety. ... show more
Reviewed in the United States on September 5, 2025 by Rich Reviews
    • Good quality and easy to install
Style: Precision Detection Size: 3-Pack Configuration: Hardwired
These were easy to install. The base is slightly smaller than the Kidde brand I replaced. So I’ll have to paint around all of them. I had to buy the adapters so no rewiring was needed. Easy for me to do. I like the way the door opens to replace batteries without having to take the whole thing off the wall or ceiling. ... show more
Reviewed in the United States on September 25, 2025 by Beth in TX
    • Purchased to mitigate false alarms
Style: Precision Detection Size: 1-Pack Configuration: Hardwired
I purchased the SM300-AC to replace the first alert 3120B which is discontinued. The 3120B was giving too many false alarms, always in the middle of the night. When I purchased the 3120B, I also purchased two, first alert 3210 smoke alarms and they have never produced a false alarm in 2.5 years. The 3210 use a 10 year battery whereas the 3210B is hardwired (both types are ionization and photoelectric). I suspect the hardwired feature was the false alarm culprit because house power fluctuates in the night. Good engineering practice would have mitigated this problem. Hopefully, First Alert has redesigned the SM300-AC to fix the false alarm issue found in the 3120B. (The SM300-AC is First Alert’s replacement for the discontinued 3120B and uses the same mounting base/ electrical connection.) I will update this review if the SM300-AC produces false alarms like the 3120B. ... show more
Reviewed in the United States on August 22, 2025 by JOSEPH KAISER
    • Good technology and very easy installation.
Style: Standard Detection Size: 1-Pack Configuration: 10-Year Battery
I recently learned that the service life of smoke detectors is about 10 years. Checking my Amazon order history, I found out ours were 12 years old. This is exactly the same model, and it took me less than an hour to put batteries in 6 of these and swap out the old ones. These are dual function (detects smoky fires via photocell, detects hot fires by ionization.) Because they are the same model, they plugged right into the existing ceiling mounts. They are also dual powered, normally by house AC, but with battery backup. I feel well protected for the next 10 years, and have made a calendar note for annual battery changes. ... show more
Reviewed in the United States on May 19, 2025 by Mike Utt
    • Dual Sensor Technology
Style: Precision Detection Size: 1-Pack Configuration: 10-Year Battery
This is a super product and easy to install.
Reviewed in the United States on September 22, 2025 by Lynn Bastian
    • Going back to Kiddie. Always chirping but never consistent
Style: Standard Detection Size: 1-Pack Configuration: 10-Year Battery
I have had these units for over a year now and they are driving me insane! I decided to replace all the original smoke detectors in my house which was built in 1996. Upon completing research, I found that Consumer Reports rates these units as the best smoke only units on the market, so I went with them. Install was seamless, replaced the pigtails and connected to house electric, no issues. About an hour after installing them, the unit in my daughters room chirped 3 times and then five minutes later it did it again, and then nothing for a couple of hours and then it did it again, 3 chirps, and then silent for the rest of the day. The next day, I heard 3 chirps come from the guest room, silent for about 15 minutes, and the 3 more chirps, then nothing for several more hours. This same issue repeats itself in the master bedroom, and my son's room (all units on the upper level of our house). According to the owner's manual, 3 chirps every five minutes means a malfunction and you should replace the unit immediately. I had just barely purchased the units and they're already malfunctioning? My issue with this is that it isn't happening every five minutes, it is completely a guess when the next chirp will be. And besides, none of the units on the main floor or basement were chirping. I replaced batteries on all units, I even undid the wiring and re-installed all the units and received the same result. I finally called First Alert and they walked me through some troubleshooting exercises and they determined that the smoke detectors are in good working condition and that there must me an issue with how my house was wired. Well, now it is one year later and the smoke detectors are still doing their thing, never consistent but I have had enough..I am switching to Kiddie brand to see if the issue continues. If it does, I will get an electrician to check it out. First Alert smoke detectors are no bueno for this house. I have 5 units on my second story and all 5 of them give a ... show more
Reviewed in the United States on October 4, 2021 by Kel
    • Very pleased after installing 7
Style: Precision Detection Size: 6-Pack Configuration: Hardwired
installed 7 in place of a bunch of firex units that were falsing. If you buy one at a time, they come with an adapter to plug right into firex connectors. if you buy the 6-pack, there's no adapter. Worked without a hitch, no falsing. We chose these because they had both photo and ion sensors and have a reputation of being a slightly higher quality device with less falsing. ... show more
Reviewed in the United States on October 7, 2025 by meep
    • Same as Unit Replaced
Style: Standard Detection Size: 1-Pack Configuration: 10-Year Battery
Fits like the OEM unit in my house easy to install. Same electrical plug.
Reviewed in the United States on October 5, 2025 by Bob G

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