---
product_id: 10703157
title: "First Alert 9120BFF/ SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, White, 1-Pack"
brand: "brk"
price: "R788"
currency: ZAR
in_stock: true
reviews_count: 13
category: "Brk"
url: https://www.desertcart.co.za/products/10703157-first-alert-9120bff-smi100-ac-smoke-detector-hardwired-alarm-battery
store_origin: ZA
region: South Africa
---

# 120V hardwired power 85dB loud alarm 9V battery backup First Alert 9120BFF/ SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, White, 1-Pack

**Brand:** brk
**Price:** R788
**Availability:** ✅ In Stock

## Summary

> 🔥 Stay ahead of danger with smart, seamless protection ⚡

## Quick Answers

- **What is this?** First Alert 9120BFF/ SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, White, 1-Pack by brk
- **How much does it cost?** R788 with free shipping
- **Is it available?** Yes, in stock and ready to ship
- **Where can I buy it?** [www.desertcart.co.za](https://www.desertcart.co.za/products/10703157-first-alert-9120bff-smi100-ac-smoke-detector-hardwired-alarm-battery)

## Best For

- brk enthusiasts

## Why This Product

- Trusted brk brand quality
- Free international shipping included
- Worldwide delivery with tracking
- 15-day hassle-free returns

## Key Features

- • **Trusted Legacy:** Backed by First Alert’s 10-year limited warranty and UL certification—decades of proven reliability.
- • **Rapid Fire Detection:** Ionization sensor targets fast flaming fires for quicker, life-saving alerts.
- • **Uninterrupted Safety:** Hardwired with 9V battery backup ensures your home stays protected even during power outages.
- • **Effortless Installation:** Gasketless mount and tamper-resistant locking brackets make setup a breeze for busy professionals.
- • **Smart Interconnectivity:** Link up to 12 compatible alarms for whole-home synchronized alerts—never miss a warning.

## Overview

The BRK First Alert 9120BFF is a hardwired smoke detector featuring a 120V power source with a 9V battery backup for continuous operation. Equipped with an ionization sensor, it detects fast flaming fires and sounds an 85-decibel alarm. It supports interconnection with up to 12 compatible devices for whole-home alerts, includes tamper-resistant mounting, and offers a 10-year limited warranty, making it a trusted, professional-grade safety solution.

## Description

Product Description Promote greater household safety with the First Alert 9120BFF Hardwired Smoke Alarm with Battery Backup. This 120 volt AC smoke detector uses an ionization smoke sensor to reliably detect smoke from hot, fast flaming fires and alerts you with a loud 85 decibel alarm. Designed to be wired directly into your home's electrical system, this hardwired smoke detector features a backup battery that helps keep the alarm functioning even in the event of a power outage. The gasket less mount helps ensure a perfect alignment for easy installation, while tamper resistant locking pins keep the alarm secure. And thanks to the convenient test/silence button, you can easily check whether the alarm is functioning properly and mute false alarms. This smoke alarm can integrate with up to 12 other First Alert or BRK hardwired alarms and features a latching indicator that identifies which unit triggered the alarm. desertcart.com Introducing the revolutionary BRK 9120 series smoke alarms which have been redesigned from the ground up. They install faster, perform better, and are even smarter than before. All of these improvements help reduce nuisance alarms and save you time and money. BRK Electronics smoke alarms are designed to be easy to install, easy to maintain, and quality-engineered for years of virtually maintenance-free service. The 9120B AC-powered smoke alarm with battery backup includes these features: Ionization sensor which helps detect fast flaming fires that consume combustible materials rapidly. 120-volt AC inter-connectable (with maximum 18 compatible devices). The alarm can be interconnected with up to 12 other compatible smoke alarms and six compatible devices like bells, horns, repeaters and door closers. If one unit triggers an alarm, all smoke alarms in the series will sound. Power indicators show which unit in the series initiated the alarm. Latching alarm indicator which automatically identifies which unit initiated the alarm. Smart technology to reduce nuisance alarms. 9-volt battery backup for peace of mind during power malfunction. Single test/silence button which both silences a non-threatening alarm or low battery warning and allows you to test the unit's functionality. Perfect mount system including a gasketless base for easy installation and new mounting bracket that keeps the alarm secure over a wide rotation range to allow for perfect alignment. Mounting bracket lock for tamper resistance. Dust cover to keep unit clean during construction. 10-year limited warranty. All BRK Electronics smoke alarms meet UL 217 standard and are listed with the California State Fire Marshal. They use the new UL mandated repeating 85-decibel alarm horn pattern. 10-year limited warranty. This unit is approved for sale in Oregon after new revisions on law HB2586.--Bree NorlanderWhat's in the Box One smoke alarm, one 9-volt battery, and user's manual

Review: Great alarm at a generic price! - It took me a long time to decide which smoke detectors to buy for my house, this model or the brand made by Kiddie. My house already had the Kiddie brand and this would mean a much faster replacement for all the smoke detectors in my house. Over time the Kiddie brand tended to chirp a lot and that drove everyone in the house crazy, especially my older and wonderful dog. My daughter said a candle lit in her room also set off all the smoke detectors in our house. If you go to the store you will find these labeled "BRK" with the words "First Alert" in smaller letters underneath and they come in a yellow and black box. It is unfortunate. Yellow and black packaging reminds me of generic food items back in the 70's and these items had a reputation for being below par. If I did not know what I was looking for I would have passed over these units in favor of something else, and I also noticed that BRK and First Alert puts their more expensive models in fancy and beautiful packaging. Thus, I fear that this company intentionally brands this "entry level" smoke detector in yellow and black to dissuade people from buying it and moving up to the more expensive models. I bought the contractor pack of this item as well as three single units to replace the nine smoke detectors in my house. All of these come with a free battery. I knew I would have to take down the old detectors, take down the mounts, and disconnect the old wiring in order that I be able to put in the new mounts and the new wiring for this smoke detector. It is a job that takes about 10 minutes at the most to completely swap out each of the units. Remember to shut off the circuit breaker! The alarm itself looks great. I like the design a lot better than the flat plastic orb. Once the new wiring harness is connected and the mount is secured to the ceiling, the new detectors snap easily into place for the wiring and you twist it onto the mount. The battery compartment is on the side and although the door for the battery looks cheap, all held up well and none broke. The alarm itself is easy to test, push the big button, and the alarm is loud enough to get anyone's attention. So far, cross our fingers, there have been no errant cheeps and no false alarms. Now to give Kiddie credit our old alarms were nearing the end of their expected lifespan so the new ones would have probably worked as well. I admit it, I went for the name brand!
Review: Good buy with a fair price - The fire detectors came fast and was easy to installed. Ended replacing two old detectors working better than the originals. Good quality. Another good thing is that the provided battery has charge. I had previous experience with other Smoke Detectors that come with weak or discharged batteries. Good buy and a fair price.

## Features

- Keep your family safe with this hardwired smoke alarm the battery backup means constant monitoring, even if there's a power failure
- Equipped with an ionization sensor, this smoke alarm reliably detects smoke from fast flaming fires and alerts you with an 85 decibel alarm
- To ensure complete protection make sure to place one on each level of your home and in each bedroom
- Can connect to other compatible BRK or first alert smoke detectors, to ensure all alarms will sound when smoke is detected
- Simple to use, with a single test/silence button, and side load battery compartment tamper resistant locking brackets and universal mounting brackets make installation easy
- Rigorously tested to meet UL standards120 volt AC power with 9V battery backup to keep alarm functioning during power outage
- First Alert has been the most trusted brand in home safety since launching the first residential smoke alarm in 1958 (Based on a First Alert Brand Trust Survey in February 2018)
- Faster turnarounds on job sites with the easy-to-install, most-trusted alarms in home safety

## Technical Specifications

| Specification | Value |
|---------------|-------|
| ASIN | B00O8MVW3U |
| Alarm | Audible |
| Assembled Diameter | 5.6 Inches |
| Batteries | 1 9V batteries required. (included) |
| Batteries Included? | Yes |
| Batteries Required? | Yes |
| Battery Cell Type | Alkaline |
| Best Sellers Rank | #960 in Tools & Home Improvement ( See Top 100 in Tools & Home Improvement ) #6 in Smoke Detectors & Fire Alarms |
| Brand | BRK |
| Color | White |
| Customer Reviews | 4.6 4.6 out of 5 stars (18,938) |
| Cutting Diameter | 5.6 Inches |
| Date First Available | June 1, 2006 |
| Global Trade Identification Number | 00029054015327 |
| Included Components | smoke detector, batteries, mount |
| Is Discontinued By Manufacturer | No |
| Item Package Quantity | 1 |
| Item Weight | 0.8 ounces |
| Item model number | 9120B |
| Manufacturer | First Alert |
| Number Of Pieces | 1 |
| Number of Items | 1 |
| Operating Humidity | 10-95% RH |
| Part Number | 9120BFF |
| Pattern | Filter |
| Power Source | Battery Powered |
| Product Dimensions | 5.6"D x 5.6"W x 2.2"H |
| Sensor Type | Ionization |
| Size | 1-Pack |
| Style | 9120BFF |
| Type of Bulb | LED |
| UPC | 029054015327 |
| Voltage | 120 Volts |
| Warranty Description | 10 Year Limited |

## Product Details

- **Alarm:** Audible
- **Brand:** BRK
- **Color:** White
- **Global Trade Identification Number:** 00029054015327
- **Item Weight:** 0.05 Pounds
- **Operating Humidity:** 10-95% RH
- **Power Source:** Battery Powered
- **Product Dimensions:** 5.6"D x 5.6"W x 2.2"H
- **Sensor Type:** Ionization
- **Style:** 9120BFF

## Images

![First Alert 9120BFF/ SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, White, 1-Pack - Image 1](https://m.media-amazon.com/images/I/71FMyNMOalL.jpg)

## Questions & Answers

**Q: How do you silence this alarm? Apparently the low battery notification only starts after midnight and WILL NOT STOP unless you have another battery.**
A: I am certain this applies to all brand and model of smoke detectors.  Once the low battery beep starts happening, which is always just as your falling off to sleep, there is only one way to stop it.  Follow the steps outlined below.
1 - put all weapons in your house under lock and key. (this is for the safety of you your family and the manufacturer of the smoke detectors).
2 - Give the key to someone you can trust and that your are not capable of overpowering.
3 - Find the smoke detector that is beeping. Tip, its never the one you are standing beneath look up at.
4 - Ice your foot because by now you have kicked several walls, doors and furniture.
5 - Assuming you have located the guilty smoke detector and have not yet burned down your home or found a way to access your weapons in step 1, move to step 6.
6 - Take the guilty smoke detector(s) into the garage and smash them into as many pieces as possible with the biggest hammer you own.
7 - Most likely you have stopped the regular beeping but every 20 to 40 minutes or so you will still hear a beep.
8 - Start a fire in the back yard fire pit and when the fire has reached white hot with glowing red hot coals put the smashed bits and pieces into the fire and let it burn until it burns out on its own.
9 - Take a shower and get dressed because by this time your late for work and haven't slept.
10 - When you get home that evening and hear another beep burn the house but make it look like an accident.

**Q: Can a  BRK Model 92120B smoke detector directly plug in and replace an old BRK Model 4120B smoke detector (without an adapter)**
A: Yes.  I just replaced 2 very old (older than 10 years) BRK Electronics Model 4120B smoke detectors with these newer First Alert/BRK Brand Model 9120B units.  My older units were yellowed with age, so I also replaced the plastic base.  I did reuse the 3 pin electrical connector, as the "old" electrical connector matches the new unit.  The new smoke detectors are functioning/self-testing normally.

**Q: can these be connected together so if one is set off they  all go off?**
A: Have these in my home. House was built about 4 years ago (2017) Came with the house.. One goes off they all go off. They are connected to each other by wire. I did have the one in my bedroom that I had to replace prematurely.  It was just going off for no reason setting the entire house alarms. It was easily identified by the light on it that it was the culprit. Basic troubleshooting taking out of system all was good. I am a 42 year volunteer firefighter,  held a Chief, Captain , Luitenant, Firefighter and other various positions . My opinion,  having them all wired together, so when one goes off they all do is SMART! Been to multiple house fires through all my years and seen where the families on the first floor watching TV while their second floor or basement is burning up. 🔥

**Q: My entire home is equipped with BRK smoke detector (4120 B) and Carbon Monox Det (CO50120B). They need replacing. Will new BRK fit extant casings?**
A: The mount screws will fit but the base plate itself is slightly smaller and you might have to touch up paint. The connectors will fit as well so no need to change those

## Customer Reviews

### ⭐⭐⭐⭐⭐ Great alarm at a generic price!
*by S***N on July 27, 2015*

It took me a long time to decide which smoke detectors to buy for my house, this model or the brand made by Kiddie. My house already had the Kiddie brand and this would mean a much faster replacement for all the smoke detectors in my house. Over time the Kiddie brand tended to chirp a lot and that drove everyone in the house crazy, especially my older and wonderful dog. My daughter said a candle lit in her room also set off all the smoke detectors in our house. If you go to the store you will find these labeled "BRK" with the words "First Alert" in smaller letters underneath and they come in a yellow and black box. It is unfortunate. Yellow and black packaging reminds me of generic food items back in the 70's and these items had a reputation for being below par. If I did not know what I was looking for I would have passed over these units in favor of something else, and I also noticed that BRK and First Alert puts their more expensive models in fancy and beautiful packaging. Thus, I fear that this company intentionally brands this "entry level" smoke detector in yellow and black to dissuade people from buying it and moving up to the more expensive models. I bought the contractor pack of this item as well as three single units to replace the nine smoke detectors in my house. All of these come with a free battery. I knew I would have to take down the old detectors, take down the mounts, and disconnect the old wiring in order that I be able to put in the new mounts and the new wiring for this smoke detector. It is a job that takes about 10 minutes at the most to completely swap out each of the units. Remember to shut off the circuit breaker! The alarm itself looks great. I like the design a lot better than the flat plastic orb. Once the new wiring harness is connected and the mount is secured to the ceiling, the new detectors snap easily into place for the wiring and you twist it onto the mount. The battery compartment is on the side and although the door for the battery looks cheap, all held up well and none broke. The alarm itself is easy to test, push the big button, and the alarm is loud enough to get anyone's attention. So far, cross our fingers, there have been no errant cheeps and no false alarms. Now to give Kiddie credit our old alarms were nearing the end of their expected lifespan so the new ones would have probably worked as well. I admit it, I went for the name brand!

### ⭐⭐⭐⭐⭐ Good buy with a fair price
*by R***E on December 14, 2025*

The fire detectors came fast and was easy to installed. Ended replacing two old detectors working better than the originals. Good quality. Another good thing is that the provided battery has charge. I had previous experience with other Smoke Detectors that come with weak or discharged batteries. Good buy and a fair price.

### ⭐⭐⭐⭐⭐ Ease of Installation
*by M***S on December 21, 2025*

This was a replacement for the same smoke detector I had installed approximately 10 years ago. All I did was climb the ladder, unplugged the old and plugged the new one in. Took 5 minutes and works perfect.

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*Product available on Desertcart South Africa*
*Store origin: ZA*
*Last updated: 2026-02-08*