--- product_id: 80051211 title: "First Alert 9120B / SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, 3-Pack" brand: "first alert" price: "€ 136.34" currency: EUR in_stock: true reviews_count: 9 category: "First Alert" url: https://www.desertcart.hr/products/80051211-first-alert-9120b-smi100-ac-smoke-detector-hardwired-alarm-battery store_origin: HR region: Croatia --- # Hardwired with battery backup Interconnects up to 18 devices Ionization sensor for fast flaming fires First Alert 9120B / SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, 3-Pack **Brand:** first alert **Price:** € 136.34 **Availability:** βœ… In Stock ## Summary > πŸ”₯ Stay ahead of danger with the smartest, fastest smoke alarm on the block! ## Quick Answers - **What is this?** First Alert 9120B / SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, 3-Pack by first alert - **How much does it cost?** € 136.34 with free shipping - **Is it available?** Yes, in stock and ready to ship - **Where can I buy it?** [www.desertcart.hr](https://www.desertcart.hr/products/80051211-first-alert-9120b-smi100-ac-smoke-detector-hardwired-alarm-battery) ## Best For - first alert enthusiasts ## Why This Product - Trusted first alert brand quality - Free international shipping included - Worldwide delivery with tracking - 15-day hassle-free returns ## Key Features - β€’ **Uninterrupted Safety ⚑:** Hardwired power with 9V battery backup ensures your home stays protected even during power outages. - β€’ **Rapid Fire Detection πŸ”₯:** Advanced ionization sensor quickly detects fast flaming fires, giving you crucial extra seconds to act. - β€’ **Seamless Connectivity πŸ”—:** Interconnect up to 18 compatible alarms and devices so every corner of your home sounds the alert simultaneously. - β€’ **Trusted Legacy Since 1958 πŸ†:** Join millions who rely on First Alert’s proven technology, rigorously tested to meet UL safety standards. - β€’ **Effortless Installation πŸ› οΈ:** Universal mounting brackets and tamper-resistant locks make setup a breezeβ€”perfect for busy professionals. ## Overview The First Alert 9120B is a hardwired smoke detector with a 9-volt battery backup, featuring an ionization sensor designed to detect fast flaming fires. This 3-pack offers interconnectivity with up to 18 compatible devices, ensuring comprehensive home coverage. Easy to install with tamper-resistant brackets and a single test/silence button, it meets UL safety standards and carries the trusted First Alert legacy since 1958. ## Description 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. Faster turnarounds on job sites with the easy-to-install, most-trusted alarms in home safety. Review: Smoke Detectors - These were a replacement for the smoke detectors that were in our home. They were easy to install and come with replacement wires if one should need them. These are hard-wired to the wall and come with batteries used for backup. Review: Easy no hassle install 9120B replacement - These are an excellent replacement for the original First Alert 9120B. I’m a single lady who owns a home I needed easy installation. I replaced two smoke detectors in 5 minutes. The prongs matched up perfectly and the mount was the perfect it. The battery was also included. No additional assembly was required. The mount and wiring is included, but I did not need them. ## Features - Keep your family safe with this 3 pack of hardwired smoke alarms; 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 standards - Faster turnarounds on job sites with the easy to install, most trusted alarms in home safety - 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) ## Technical Specifications | Specification | Value | |---------------|-------| | ASIN | B07B4CG1PG | | Best Sellers Rank | #222 in Tools & Home Improvement ( See Top 100 in Tools & Home Improvement ) #2 in Smoke Detectors & Fire Alarms | | Brand | First Alert | | Built-In Media | 9-volt battery (3), First Alert BRK 9120B Hardwired Smoke Alarms with Battery Backup (3), Mounting brackets with hardware (3) | | Color | White | | Customer Reviews | 4.7 out of 5 stars 4,630 Reviews | | Global Trade Identification Number | 00029054018489 | | Item Dimensions D x W x H | 1.9"D x 5.6"W x 5.6"H | | Item Type Name | Hardwired Smoke Alarm with Backup Battery | | Item Weight | 9.6 ounces | | Manufacturer | First Alert | | Mfr Part Number | 9120BFF-3 | | Model Number | BRK 9120B-3 | | Number of Items | 3 | | Power Source | Battery Powered,Hardwired | | Product Dimensions | 1.9"D x 5.6"W x 5.6"H | | Product Style | Standard Detection | | Sensor Type | Ionization | | Style | Standard Detection | | UPC | 029054018489 | | Unit Count | 3 Count | ## Product Details - **Brand:** First Alert - **Color:** White - **Global Trade Identification Number:** 00029054018489 - **Item Weight:** 0.6 Pounds - **Manufacturer:** First Alert - **Number of Items:** 3 - **Power Source:** Battery Powered,Hardwired - **Product Dimensions:** 1.9"D x 5.6"W x 5.6"H - **Sensor Type:** Ionization - **Style:** Standard Detection ## Images ![First Alert 9120B / SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, 3-Pack - Image 1](https://m.media-amazon.com/images/I/61LPi-3y2tL.jpg) ## Available Options This product comes in different **Pattern, Size, Style** options. ## 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. πŸ”₯ **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 ### ⭐⭐⭐⭐⭐ Smoke Detectors *by J***Y on July 19, 2026* These were a replacement for the smoke detectors that were in our home. They were easy to install and come with replacement wires if one should need them. These are hard-wired to the wall and come with batteries used for backup. ### ⭐⭐⭐⭐⭐ Easy no hassle install 9120B replacement *by T***Y on June 12, 2026* These are an excellent replacement for the original First Alert 9120B. I’m a single lady who owns a home I needed easy installation. I replaced two smoke detectors in 5 minutes. The prongs matched up perfectly and the mount was the perfect it. The battery was also included. No additional assembly was required. The mount and wiring is included, but I did not need them. ### ⭐⭐⭐⭐⭐ Easy to install. *by R***. on May 17, 2026* Worked very well! Easy to install. Battery included. Noneed to order batteries. ## Frequently Bought Together - First Alert 9120B Smoke Detector, Hardwired Alarm with Battery Backup, 3-Pack - BRK First Alert 9120BFF/ SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, White, 1-Pack - First Alert 9120B Smoke Detector, Hardwired Alarm with Battery Backup, 6-Pack --- ## Why Shop on Desertcart? - πŸ›’ **Trusted by 1.3+ Million Shoppers** β€” Serving international shoppers since 2016 - 🌍 **Shop Globally** β€” Access 737+ million products across 21 categories - πŸ’° **No Hidden Fees** β€” All customs, duties, and taxes included in the price - πŸ”„ **15-Day Free Returns** β€” Hassle-free returns (30 days for PRO members) - πŸ”’ **Secure Payments** β€” Trusted payment options with buyer protection - ⭐ **TrustPilot Rated 4.5/5** β€” Based on 8,000+ happy customer reviews **Shop now:** [https://www.desertcart.hr/products/80051211-first-alert-9120b-smi100-ac-smoke-detector-hardwired-alarm-battery](https://www.desertcart.hr/products/80051211-first-alert-9120b-smi100-ac-smoke-detector-hardwired-alarm-battery) --- *Product available on Desertcart Croatia* *Store origin: HR* *Last updated: 2026-08-09*