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BRK 9120B Smoke Alarm, Dual Ionization, 120V Hardwired w/ Battery Backup

Brand: BRK
Model: 9120B
Condition: New
Warranty: 10 Years
SKU: 90101
4.8 (18 Reviews)
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BRK 9120B Smoke Alarm

Regular Price: $11.10
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$7.77 /ea

The BRK 9120B smoke alarm is a great choice when it comes to affordability. Redeigned from the ground up, BRK created the 9120B model to directly replace past BRK smoke alarms while greatly improving sensing technology, installation ability, and improved connectivety. The first alert 9120B smoke alarm has an 85dB horn, 9V battery back-up and a silence feature.

The BRK 9120B smoke alarm uses dual ionization technology to reduce false alarms more efficiently and more accurately than ever before. The 9120B smoke alarm is designed for sleeping rooms in your home, hospitals, hotels, motels, college dormatories and multi-family housing units. This BRK smoke alarm complies with NFPA101, UL217, CSFM, NFPA72, HUD, FHA, and other agencies. Where AC/DC silent smoke alarms are required, BRK smoke alarms work perfectly.

The BRK 9120B model has the ability to be interconnected within a circuit of alarms and other alert devices such as bells, whistles, repeaters, fans, or switches. You can connect up to 17 BRK devices of which 11 can be smoke alarms, and 6 can be alternate devices! Integrated within the BRK 9120B smoke alarm is a 9V battery backup to make sure your smoke alarm does not loose operation when power fails which providing added security and peace of mind.

All around, BRK smoke alarms are the perfect choice if you are looking for affordability, function, and ease of use.

BRK Smoke Alarm Replacement

This BRK Electronics 9120B smoke alarm is the direct replacement for the discontinued BRK smoke alarm models 4120B, 4120SB, 4919 and 86RAC. Wiring harness and communication protocol is the same across BRK models (i.e. a 4120B will talk to a 9120B). When replacing an older smoke detector, only the mounting bracket needs to be changed.

About BRK Smoke Alarms

For over 50 BRK smoke alarms have been the preferred smoke alarm to protect lives. BRK makes hardwired, battery operated, and plug-in smoke alarms for professionals, remodeling, homeowners. Designed for easy installation, easy mainatenance. Many BRK smoke alarm models can be interconnected with their patented OneLink® and has quickly become the preference for contractors. Many of BRK smoke alarms 

  • 120 VAC; Interconnectable
  • 9V Battery Included
  • AC Power Indicator
  • Alarm Indication
  • Battery Activation Tab
  • Battery Back-Up
  • Battery Drawer Lock
  • Easy Install Mounting Bracket
  • Ionization Sensor
  • Low Battery Warning "Chirp"
  • Missing Battery Tab
  • Mounting Bracket Lock
  • Quick Plug-In Power Connector
  • Swing-Open Battery Door
  • 120V AC
  • Alarm Dimensions: 5.6" dia x 2.0" H
  • Audio Alarm: 85dB at 10 feet
  • Humidity Range: 10 percent to 90 percent relative humidity (RH)
  • Operating Current: .04 amps (standby/alarm)
  • Operating Voltage: 120V AC 60Hz w/ 9V battery backup
  • Temperature Range: 40 Degree F (4 Degree C) to 100 Degree F (38 Degree C)
  • Weight: 7.8 oz (9120B)
10-year warranty through BRK Electronics
Customer Reviews

High quality and good value

These smoke detectors are compatible with the ones the contractor installed when my house was new. BRK/First Alert has kept the same mounting bracket and wire connector so I don't need any tools--just untwist, slip off the wire connector and plug it into the new one. My combination CO/smoke detectors need to be replaced every 7 years so I just order these smoke only detectors at the same time, even though they are rated for 10 years. High quality and good value. Love the ease of replacement.


on 03-23-2017 by Zippy

.Thanks to Westside and those who have commented

Found info on replacing my failing BRK 86RAC units here. The 9120B worked perfectly, and your site saved me a bunch. One was $35 at Home Depot. Here I got 4 incl shipping for $40. And batteries are included. Thanks much.


on 01-12-2017 by airpizz6

Good quality product

One of the go to hardwired smoke alarms!


on 01-29-2016 by MMC

100% satisfied.

I ordered 970 smoke detectors (BRK9120B) all were in good working condition none of these had to be sent back or replaced even the batteries are holding up which was very surprising to me because usually I get low quality batteries that have been in a warehouse for 10 years when I buy an item with batteries already installed. I was 100% satisfied with this purchase.


on 11-16-2015 by Ronald

Easy replacement and reasonable

My original BRK smoke alarms started acting up after about 10 years. Only then did I find out that smoke alarms have a lifespan of about 10 years and should be replaced. These were perfect replacements for what I had, and have worked perfectly (no chirping) since I installed them.


on 11-02-2015 by Joe

Almost 1/2 Price!

These were the same electrical connector as my1996 models which I replaced 7 of. What a great price!! $15 at Home Depot each, $8 brainer. Even bought a spare and shipping was still less than Home Depot by $32! Smoke alarms shipped in three days!


on 03-08-2015 by DirtyHarry

good product

Easy to install can be interconnected with others smoke detectors in bedrooms and hallways and on each level of your house. Wired 120 volt and battery backup makes these very dependable to protect your family.


on 10-24-2014 by Doug

i think it is really good

it is excellent, it can detected smoke fast, it really help to maintain protected from fire.


on 09-18-2011 by eli

Easy to Install but . . .

Great service and price from Westside. Got these to replace outdated contractor-installed alarms. These installed easily on existing mounting rings and electric pigtails connected right to existing connectors. But these alarms are susceptible to spiders getting inside and setting off false alarms, usually in the middle of the night. While the case protecting the ionization detector has slots to prevent bugs from having direct access, small spiders get in through the gap between the mounting ring and the alarm case and set off the alarms. With the alarms being interconnected, the middle of the night the spider-induced alarms' sounding is, well, alarming. Then it''s usually necessary to take down the alarm with the problem and shake it vigorously to get the spider out.


on 07-29-2011 by Kawasaki Biker

Difficult to replace battery

These were installed in a newly built house that we bought in 2007. The only problem I have is that inserting the battery is very difficult. Otherwise I would give it 5 stars for quality.


on 02-16-2011 by Florida gal


Replaced 3 BRK 86RAC smoke alarms with 3 new BRK 120V Hardwired 9120B models. They ARE a direct replacement for the old ones, same plug ins. Out of the box, put up new brackets, old screws aligned perfect, plugged in, and pulled the battery tag. Did all three in less than ten minutes. Also received on delivery date, could not have been more simple. Outstanding!!!!


on 12-31-2010 by RFH

mon a mi

bonjour. what is for us is different than the states. we find these and buy for to change our old one. thank you for this. Ciao


on 02-17-2010 by Georges

this is right

part of the problem was that no one knew that this would work. after we called westside they shipped these to us and we installed them. so far, no issues. I guess as far as smoke detectors go, their sort of cute. much better than the old yellow ones that we had up there. I'm not even sure if they make them anymore.


on 02-17-2010 by Jennifer

pretty good

we have the old ones and now we have the new ones and this is what we need. PJ installed them in all the rooms and then came back to tell me and I was surprised. He installed them so quickly. I was on this website looking for the shower heads and i see that this is what looks like I have. I think that maybe this is the best one on the market because i don't like cheap things.


on 02-17-2010 by Mr. Patel


I wish that I had known these were here. This is exactly what I needed. The connector is the same and thats important


on 02-17-2010 by Sussie LImpkin

Great deal

I recently purchased 8 of these units for my home. They installed in minutes and work great!


on 02-03-2010 by Howie

direct plug in replacment

Had to repalce all the smoke alarms in my 15 year old house. These are direct replacment for the older RK alarms. Just had to change out the plastice mounting rings and they plugged directly into the original plug, no wiring changes. The units will tell y9ou which alarm is causing the alarm. The older ones took troubleshooting to find the offending unit.


on 05-10-2009 by PeteExcellent rplacement better technology

Talk about easy installation!

I recently had to replace my old 4120B. It took me 15 minutes to get it wired up and in the ceiling. At this price I might as well replace them all since its so simple.


on 02-19-2009 by Ethan

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