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FIRST ALERT SC9120B Corded Electric Combination Alarm with Adapter Plugs for Easy Replacement

Based on 874 reviews
Condition: New
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$61.97
Holiday Deal · 31% off was $89.95

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Availability: 12 left in stock
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Arrives Friday, Nov 20
Order within 19 hours and 58 minutes

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At a glance

Condition
New
Style
Hardwired
Pattern
Alarm
Model
SC9120B
Dimensions
0.07"D x 0.22"W x 0.22"H
Weight
10.08 oz
Color
white

Features 8

  • Convenient adapter plugs makes it easy to replace existing hardwired alarms without needing to rewire
  • Keep your family safe with this hardwired First Alert smoke and carbon monoxide alarm with a 10-year battery backup, which means constant monitoring for the life of the alarm, even if there's a power failure
  • Combination smoke alarm and carbon monoxide detector features electrochemical carbon monoxide sensing technology, as well as intelligent smoke sensing technology to reduce nuisance alarms
  • Indicator lights on the face of the unit display the presence of smoke or carbon monoxide, while an 85-decibel siren provides a clear, loud warning upon detection

Description

This First Alert hardwired smoke alarm and carbon monoxide detector features an ionization smoke sensing chamber and an electrochemical carbon monoxide sensor. Installation and connection to AC power is easy with the included adapter plugs and "quick-connect" wiring harness so you can you easily replace existing hardwired alarms without needing to rewire. The 10-year battery backup allows for continued monitoring for the life of the alarm. Intelligent sensing technology is designed to reduce nuisance alarms; one button silences them if they do occur, and also tests detector functions. The latching alarm indicator automatically identifies which unit initiated the alarm, even after the conditions that set it off have subsided. And an end-of-life signal enhances your safety by letting you know when it's time to replace the unit. Connect it to compatible BRK or First Alert alarms within a single-family residence; connecting will sound all the alarms together.

Specs 21

Brand First Alert
Style Hardwired
Power Source Corded Electric
Color white
Product Dimensions 0.07"D x 0.22"W x 0.22"H
Item Weight 10.08 ounces
Alarm Audible
Operating Humidity 10-95% RH

Frequently asked questions

If you place your order now, the estimated arrival date for this product is: Friday, Nov 20

Yes, absolutely! You may return this product for a full refund within 30 days of receiving it.

To initiate a return, please visit our Returns Center.

View our full returns policy here.

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Top Amazon Reviews


First Alert SC9120B gets 5 stars
Style: Hardwired Pattern Name: Alarm
This First Alert model SC9120B smoke/CO alarm replaces a similar 10 year old unit that recently failed. The unit came with spare installation hardware that wasn't needed for my application. The new unit swapped in easily and tested Good. Completely satisfied with the unit
Reviewed in the United States on August 12, 2026 by Jake

Perfect replacement for my wired combination Smoke/CO alarm
Style: Hardwired Pattern Name: Alarm
My old combination alarm had reached the end of its functional life. It would not stop the intermittent beeping even with fresh batteries. I was able to find the exact match on Amazon. No more annoying false alarms. The wire connections were perfect, just plug and play.
Reviewed in the United States on July 14, 2026 by Amazon Customer

Smoke detector/carbon dioxide alarm
Style: Hardwired Pattern Name: Alarm
The smoke detector and carbon dioxide alarm was exactly what we needed.
Reviewed in the United States on August 17, 2026 by Amazon Customer

Good Deal
Style: Hardwired Pattern Name: Alarm
Easy to installation to replace non-functioning unit.
Reviewed in the United States on September 2, 2026 by Sharon Hughes

No problems with install
Style: Hardwired Pattern Name: Alarm
Replacement, worked from the install. Very happy. Ordered exact part no. Of failed unit.
Reviewed in the United States on January 3, 2026 by DKF

Perfect Fit
Style: Hardwired Pattern Name: Alarm
Arrived on schedule. I was initially alarmed to see the original box that contained the alarm was opened, part of the opening flap was missing/torn. ( could this be a return-item which would account for the missing flap and tape, and lose contents inside with no separator or cushioning ). The original box was shipped inside the Amazon box. The alarm ( with stamped manufacture date of April, 2026) looked alright and the wirings,etc. & user's manual were included in the box. I picked this seller ( more expensive than others) for the 30 day return policy...just in case it wouldn't fit my current wired plug and mounting bracket . This new alarm is a replacement for my old First Alert Model no. SC9120B that decided to retire. Glad to report that it's a perfect fit, i.e. I didn't have to redo the wiring and didn't have to replace the mounting bracket; battery was included. All's well. ... show more
Reviewed in the United States on September 9, 2026 by Cynthi C.

It works
Style: Hardwired Pattern Name: Alarm
Easy installation; it works.
Reviewed in the United States on September 17, 2026 by Richard H. Thomas

Smoke alarm
Style: Hardwired Pattern Name: Alarm
Perfect works great
Reviewed in the United States on September 18, 2026 by Amazon Customer
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