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Hardwired Combo Smoke & Carbon Monoxide Alarm w/ Battery Backup

The First Alert SC9120LBL Hardwired Combination Smoke/CO Alarm connects directly to your home electrical system. In the event of a power outage, the smoke/CO alarm is equipped with a 10 year lithium battery-backup. Integrating a Smart Technology system will reduce the likelihood of nuisance alarms triggering. A Latching Alarm Indication will remember which unit initiated an alarm. The perfect mount system features a gasketless base and a mounting bracket that keeps the alarm secure over a wide rotation range to allow for true alignment. Under normal conditions, you should not have to replace the battery for the life of the alarm.

Detects Smoke and Carbon Monoxide

Designed to meet the latest construction requirements, the First Alert Combination Smoke and Carbon Monoxide Alarm detects two threats: smoke and carbon monoxide. Lights on the face of the alarm will tell you what the threat is, and false alarms can be silenced with a single button.

Intelligent Sensing Technology Minimizes False Alarms

People sometimes disable a fire detector when it goes off due to cooking smoke or steam, even though in doing so they endanger themselves and their loved ones. Intelligent Sensing Technology is designed to distinguish between real fires and nuisances. This reduces the likelihood of false alarms significantly.

10-Year Lithium Battery Backup

The First Alert SC9120LBL Hardwired Combo Smoke and CO Alarm features a built-in 10-year lithium battery backup that provides continuous power for the life of the detector. An end-of-life timer lets you know when the device should be replaced.

Connect to Other Alarms for Greater Coverage

This hardwired combination smoke and carbon monoxide detector can be connected to other compatible BRK or First Alert CO smoke detectors within a single-family residence. Once one alarm is triggered, all connected CO smoke alarms will sound. The latching alarm indicator on the CO smoke alarm automatically identifies which unit initiated the alarm–even after the conditions that set off the alarm have subsided.

Easy to Install and Maintain

The First Alert Combination Smoke and Carbon Monoxide Alarm integrates with existing wiring and features a universal mounting bracket that makes installing the unit quick and easy. Connection to AC power is simple with a Quick Connect wiring harness.

First Alert BRK Brands Hardwired Combo Smoke & Carbon Monoxide Alarm SC9120LBL

How to Install First Alert SC9120LBL Hardwired Combo Smoke & Carbon Monoxide Alarms:

In this guide, we'll be showing you how to install First Alert Hardwired Smoke and Carbon Monoxide Alarms. Here are a few items you'll need before starting the installation process: Needle-nose pliers or utility knife, screwdriver, wire stripper, wire nuts and a ladder.

Hardwired Smoke or Carbon Monoxide Alarm Requirements:

  • 120V household electrical circuit (unswitched 120VAC)
  • Standard wiring junction box to a 4 in. (10 cm) size, on either the ceiling or wall
  • Selecting an appropriate location to install your smoke and carbon monoxide alarms (see below guidelines for additional information):
    first alert smoke alarm install guide
    • When installing an alarm on the wall, the top edge of an alarm should be placed between 4 in. (100 mm) and 12 in. (300 mm) from the wall/ceiling line.
    • When installing an alarm on the ceiling, place the alarm as close to the center as possible.
    • In either case, install the alarm at least 4 in. (100 mm) from where the wall and ceiling meet.
    • First Alert Smoke Alarm FAQs
    • First Alert Carbon Monoxide Alarm FAQs

Connecting First Alert Hardwired Alarms to 120V Wiring

To begin, turn off power at the junction box and connect your alarm to the building's electrical wiring.

  1. Locate the junction box and turn off power
  2. Remove the power connector from the new alarm's packaging
  3. Using wire nuts, attach the hot (black), neutral (white), and interconnect (orange) wires
first alert smoke alarm hardwired install guide
first alert wired in smoke alarm install guide
Black wire
Attach to black wire on power connector
White wire
Attach to white wire on power connector
Orange wire

Standalone (single-station) alarm: This wire is not needed; tuck the orange wire into the junction box.

Interconnected alarms:

  • Strip 1/2 in. from the orange wire on the connector
  • Use a wire nut to attach it to the orange wire in the junction box (see image below).

Mounting First Alert Hardwired Alarms

  1. Secure the mounting bracket to the ceiling or wall using screws (included in the package)
  2. Insert the power connector into the plug on the back of your alarm
  3. Tuck any hanging wires into the junction box
  4. Position the base of the alarm onto the bracket and turn it clockwise until it's secured
  5. Remove the pull-tab to activate the backup battery
first alert carbon monoxide alarm install guide
first alert smoke and co detector install guide

Installing Additional and/or Interconnecting First Alert Hardwired Alarms

If you are installing more smoke or carbon monoxide alarms, you'll want to repeat the process throughout the building. Interconnected smoke and co alarms must meet all requirements:

  • The same fuse or circuit breaker must power all interconnected alarms.

  • Up to 18 compatible detectors can interconnect, with a limit of 12 smoke alarms.

  • The total length of wire interconnecting the alarms should be less than 1,000 ft. (300 meters). This type of wire is commonly available at hardware and electrical supply stores.

  • All wiring must conform to all local electrical codes and NFPA 70 (NEC). Refer to NFPA 72, NFPA 101, and your local building code for more information.

  • Interconnect wiring diagram:

first alert alarm install guide

If you have any doubts or reservations about these interconnect requirements, please contact an experienced electrician to install your wiring and hardwired alarms.

Restoring Power and Testing Hardwired Alarms

Once you've installed your hardwired alarms, you'll want to restore power to the junction box. Under regular operation, the power indicator light on the alarm will shine/blink to indicate that it is receiving AC power.

Here's how you can test standalone or interconnected alarms:

  • Standalone Alarms: Press and hold the Test/Silence button until the unit triggers an alarm.

  • Interconnected Alarms: Press and hold the Test/Silence button until the first unit triggers an alarm. All interconnected detectors should sound off. Repeat this process to test each alarm in the interconnected series.

Product Details
  1. Smoke particles of varying number and size are produced in all fires. For maximum protection, use both ionization and photoelectric sensing technologies. Ionization alarms are generally more sensitive to fast flaming fires and photoelectric alarms are generally more sensitive to smoldering fires.
Product Specs
Combo Smoke & Carbon Monoxide Alarms
Product Manuals

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SC9120LBL customer reviews

Overall Rating

30 Reviews
30 customers recommend this product
BRK Hardwired Combo Smoke and Carbon Monoxide Alarm with 10-Year Battery Backup Reviews
Pedro R
October 29, 2021
Verified Purchase

No need to climb ladders again to change batteries every 6 months. Product fitted perfectly on replacement smoke detector brackets.

Edward Z
July 31, 2021
Verified Purchase
Every 10 years

The exact product that I was looking for. Replaces 10 year old smoke alarm only devices. This time with with 10-year life batteries. A score for being forward thinking and safety conscious by not having to climb up and down ladders twice a a year to replace batteries. These are all 120V devices and interconnected with other First Alert/BRK devices. Installation was a breeze since the wiring is exactly the same as the previous devices.

Bruce R
May 20, 2021
Verified Purchase
No More Battery Changouts!

These alarms installed very easily to replace the similar FirstAlert alarms I had that had 9-volt battery backup electric adapter was the same, twisted right into the existing space. But now, no more battery changes until I have to replace them 10 years from now very happy!

Victor Galande
February 17, 2021
Verified Purchase
Easy install

House came with 9120B AC powered smoke detectors. Ordered replacements since its been over 10years and decided to upgrade 2 locations to a CO combo unit. So glad that I was able to use existing cabling for the SC9120LBL, as well as the smoke only model. Install for all 7 locations was under 30minutes.

Victor Galande
February 16, 2021
Verified Purchase
Easy install

House came with 9120B AC powered smoke detectors. Ordered replacements since its been over 10years and decided to upgrade 2 locations to a CO combo unit. So glad that I was able to use existing cabling for the SC9120LBL, as well as the smoke only model. Install for all 7 locations was under 30minutes.

Wayne Marquardt
June 16, 2020
Verified Purchase
First Alert product review

I'm replacing my old hard wire battery operated smoke detectors with new detectors that are guaranteed for 10 years with no climbing up and down ladders every 6 month. Well worth the investment for a 10 room townhouse. It took no time to replace and install them.

Fran Loiacono
January 24, 2020
Verified Purchase

Good company, good product good service.

David Spacone
January 7, 2020
Verified Purchase

Nice that they fit in the older model template

Mohammad Alhammadi
October 14, 2019
Verified Purchase

One of the top and best Choice in the market. So proud and happy

Kenneth Numerowski
August 29, 2019
Verified Purchase
first purchase

First time I bought from this manufacturer the pricing was good, selection was good and the product was delivered quickly.

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