First Alert Wireless Interconnect Hardwired Smoke Alarm - SA521CN-3ST (1039830)

  • First Alert Wireless Interconnect Hardwired Smoke Alarm - SA521CN-3ST (1039830)
  • First Alert Wireless Interconnect Hardwired Smoke Alarm - SA521CN-3ST (1039830)
  • First Alert Wireless Interconnect Hardwired Smoke Alarm - SA521CN-3ST (1039830)
  • First Alert Wireless Interconnect Hardwired Smoke Alarm - SA521CN-3ST (1039830)
Photoelectric Wired In Interconnected Smoke Detector
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Estimated In Stock date is 9/30/2020.
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Wireless Interconnect Hardwired Smoke Alarm

The First Alert SA521CN-3ST Interconnected Smoke Alarm allows owners to create an interconnected fire alarm system without the cost and hassle of wiring. Use this smoke detector to replace an existing hardwired smoke alarm and then install additional First Alert Wireless alarms for an interconnected safety network (additional alarms sold separately). This hardwired smoke detector can connect and communicate with up to 18 compatible alarms, so when one alarm is triggered, the entire system reacts. An integrated battery backup ensures the smoke alarm continues to work even during power outages.

Photoelectric Sensor Warns of Smoldering Fires

The First Alert Wireless Interconnect Smoke Alarm comes equipped with a photoelectric sensor to provide the earliest possible warning of fire. The sensor is optimized to detect larger smoke particles produced by smoldering fires, such as those caused by unextinguished cigarettes. It also distinguishes between real threats and smoke/vapor produced during showering, cooking, and other everyday activities, helping minimize the number of false alarms. A patented smoke entry system helps ensures reliable detection by providing a direct air pathway to the sensor.

Interconnectivity for Larger Areas

The hardwired smoke alarm can be connected to other compatible BRK and First Alert hardwired alarms for larger buildings such as dormitories, office buildings, and apartments. Connect up to 18 compatible devices: up to 12 smoke alarms and six compatible devices like horns and repeaters. First Alert helps you create a comprehensive warning system for you and your property.

Battery Backup for Continuous Coverage

In the event of a power outage, the smoke alarm is still able to function thanks to its two AA backup batteries. An indicator sound is emitted when the batteries need to be replaced. The inclusion of an optional drawer and mounting bracket lock will discourage tampering.

Test and Silence Button

Mute Button has been included to serve the dual purpose of silencing nuisance alarms and testing the functionality of your alarm.

EZ-Access Battery Door

The addition of an EZ Access Battery Door removes the hassles and burdens associated with changing your alarm's batteries.

First Alert Wireless Interconnect Hardwired Smoke Alarm SA521CN-3ST

Wireless Interconnect Hardwired Smoke Alarm Features:

  • Wireless inter-connectivity, wirelessly connect up to 18 interconnect alarms in your home and when one sounds, they all sound for increased whole-home protection.
  • 120v ac hardwired, easily replace one existing hardwired alarm with First Alert SA521 alarm and then add Wireless Interconnect battery operated alarms to connect wireless alarms with hardwired alarms--when one sounds, they all sound.
  • Battery backup provides consistent protection for added safety during power outages.
  • Photoelectric smoke sensing provides optimal protection from smoldering fires, while reducing false alarms like those caused by cooking fires and shower steam.
  • Mute button silences unnecessary alarms immediately. It also tests alarm function with same button.
  • Eco-friendly, completely recyclable as an electronic device.
  • EZ access battery door, no need to remove alarm from ceiling to change battery.
  • Optional theft-prevention lock, when activated, batteries and/or alarm cannot be removed without proper tools.
  • 2AA batteries included.
  • Loud 85db alarm.
  • Smoke alarms should be replaced every 10 years for maximum protection.
  • Meets UL217 standard.
  • FCC compliant.
  • 10 Year Limited Warranty.
  • Product Dimensions (LxWxH): 5 x 2 x 5 in.
  • Product Weight: 1 lb.
Product Specs
Write A Customer Review Review


Average score based on 45 reviews

Rating: 4.8/5Rating: 4.8/5Rating: 4.8/5Rating: 4.8/5Rating: 4.8/5

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Wireless Interconnect

Reviewed: 05/19/2020 by Tom Bijak

Works as advertised. Shipped as promised.

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5

Reviewed: 12/20/2019 by Shirley Hufford

This item did what was expected. It allowed us to connect all of our wireless smoke and carbon monoxide detectors together.

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Smoke alarm

Reviewed: 09/25/2018 by Alan Del Rossa

Tested good. Synced to other smoke alarm.

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Works well

Reviewed: 05/31/2018 by Bryan

It was easy to install since we had older BRK / First Alert units. Connected with the other units flawlessly.

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Awesome product

Reviewed: 01/05/2018 by William Rogers

This product installation is quick and easy. The set up is very labor efficient. This product is loud and will notify you immediately. This is a very good system and needs to be put out to people to let those know about it without alarm systems. Pricing is very reasonable.

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Expanded Home System

Reviewed: 05/15/2017 by Thomas Piorkowski

I had old smoke alarms that I wanted to replace: 2 upstairs, 1 main floor and 1 in the basement. Three I replaced with combo smoke/CO2, the 2nd upstairs unit I purchased a bridge unit to connect the old hard wired to the 4 new battery units. The hardest part was the wired units because the old connectors didn't match any brand of new unit. The detectors came with easy directions and it wasn't that hard. Once set up, all work perfectly together. I like the voice indication, telling you where the fire or co2 issue is located. I am very pleased with the purchase and feel more comfortable with my expanded zone. No extra cost for wiring so although the units are a little more expensive it doesn't cost as much as an electrician!

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Great Product

Reviewed: 05/15/2017 by rick christoffersen

Hardwired systems seamlessly integrated with the multiple First Alert wireless smoke alarms we installed. Now all alarms are integrated throughout our home. Awesome!

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5

Reviewed: 05/08/2017 by rick christoffersen

Great product. We integrated with 8 other Wireless Smoke Alarms. All linked perfectly together as advertised and we now have comfort of knowing any alarm activation will set off alarms throughout the house.

Rating: 4/5Rating: 4/5Rating: 4/5Rating: 4/5Rating: 4/5Had some programming problems

Reviewed: 12/16/2016 by Charles Hinton

For some reason it was hard to link this one. I have used them before and never had a problem till now. It worked in the end

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5

Reviewed: 12/05/2016 by Barbara Clark

The quality of this product is very good and responds to my needs.

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Easy whole house protection

Reviewed: 11/22/2016 by James Davis

It was very simple to sync all the smoke alarms in our home. Now we are comforted knowing that if a fire starts in the basement, we will know about it instantly 2 floors above in our bedroom.

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5

Reviewed: 06/27/2016 by Dale Welch

I spoke with someone in technical support on a Sunday who was extremely helpful in advising me which products to buy to make my house compliant for a house sale. I ordered 5 products. They all arrived on time and in good shape. They were very easy to install and all worked immediately.

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Always Works perfect

Reviewed: 04/25/2016 by Charles Hinton

Always Works perfect

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Simple solution

Reviewed: 03/30/2016 by Charles Hinton

Works perfect

Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Rating: 5/5Works everytime

Reviewed: 01/21/2016 by Charles Hinton

I have purchased many of these and they always work. Easy to program.

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Q: What is a mesh network and how do the First Alert Wireless Interconnect smoke detectors intercommunicate?
A: First Alert Wireless Interconnect smoke alarms operate on a "mesh network" to integrate smoke alarms for better safety and response in an emergency. All of the First Alert Wireless Interconnect alarms send, receive and resend the initiating alarm's signal. Why is this important? Let's say the signal is blocked from reaching the master bedroom alarm either by distance or some obstruction in the home. With First Alert Wireless Interconnect, the mesh network of alarms re-routes and re-sends the signal via the other alarms, providing a greater chance all alarms will receive the signal. The "mesh network" is a more reliable means of wireless communication.

Q: What is the proper placement of smoke alarms?
A: It is important that you have the proper placement for your smoke alarms. Install your alarms at least 20 feet from appliances like furnaces and ovens, which produce combustion particles. Alarms should be at least 10 feet from high humidity areas like showers and laundry rooms, and at least 3 feet from heat/AC vents. Be sure to install a smoke alarm in each bedroom, one at the top of each stairwell, and one on every level.

Q: My smoke alarm keeps chirping and beeping. Why does my smoke alarm chirp intermittently?
A: It is likely that the reason your smoke alarm keeps chirping and beeping is that the battery is low. Whenever your smoke alarm keeps chirping, replace the battery immediately.

Other reasons include: It could be a different device or appliance such as a security system, monitor, carbon monoxide alarm, or other device which has a similar low battery or alert signal. Some of the same factors that cause unwanted alarms can cause intermittent alarms: dust and insects in the alarm or power interruptions in hardwired alarms. Improper wiring on AC or AC/DC smoke alarms. AC alarms will chirp every 5 seconds if the interconnect wire is grounded. The orange interconnect wire should NEVER be grounded; it should only be used to interconnect other smoke alarms or compatible devices.

Q: Why doesn't my smoke alarm sound when I push the test button?
A: It is important that you frequently test your smoke alarms. When you are testing your smoke alarm, there are a number of reasons why the alarm might not sound:
  • You may not be holding the test button down long enough. Try holding it down for up to 10 seconds (20 seconds on photoelectric models) .
  • Your battery may not be installed properly or snapped all the way in place. Even if the alarm sounded briefly when the battery touched the terminals, you still need to make sure it is snapped securely in place. If the battery is loose, in cannot power the smoke alarm properly. After installing new batteries, be sure to test your smoke detector.
  • Your AC power may not be on. AC and AC/DC units will have a power indicator light (red or green) that shines continuously when they are receiving electrical power.
  • If you have a 10-Year model, the smoke alarm may not have been properly activated. If the tab broke away before the alarm was activated, you can use a toothpick to move the switch over to test the alarm.

Q: Why does my smoke alarm go off when I install a battery or turn on the AC power?
A: It is normal for smoke alarms to go off and sound briefly (up to 5-10 seconds) when you install a new battery or when they are powered up. If the alarm continues to go off and no smoke is present, the cause may be one of the following:
  • There may be insufficient battery power, try new batteries.
  • Problems with voltage or insufficient electrical power (brown out) may cause a continuous weak sounding alarm. For AC or AC/DC models, temporarily disconnect power at the service panel until the brown out is over. If you do not restore the AC power, your smoke alarms cannot warn you of a fire.
  • Incompatible warning device. If an incompatible alarm or auxiliary device is linked into a series of AC or AC/DC smoke alarms it may cause the system inadvertently go off.

Q: My smoke alarm keeps chirping, even with a new battery. What is causing this?
A: There are a number of possible causes for your smoke alarm to keep chirping even with a new battery.
  • It is possible that your smoke alarm "silence" button was pushed by mistake. The alarm will now "chirp" once a minute for up to 15 minutes before resetting.
  • Are you sure it's the smoke alarm? Funny to ask, but other devices have similar low battery chirps or warning tones.
  • Your "new" batteries may not be fresh. If batteries are stored, especially in cold areas like refrigerators, they lose their charge more quickly. Always check the freshness date on the package when buying new batteries. Keep plenty of replacement batteries on hand so that you are sure to always be protected by your smoke alarms.

Q: I lost my First Alert smoke alarm owner's manual. How can I get a new one?
A: First Alert smoke alarm owner's manuals are available online for download at no cost. Find your alarm in our Smoke Alarms section.

Q: Why does the National Fire Protection Association (NFPA) recommend that home smoke alarms be replaced after 10 years?
A: Smoke alarms have a limited life. Although each smoke alarm and all of its parts have passed many stringent tests and are designed to be as reliable as possible, any of these parts could fail over time. Therefore, you must test the devices weekly. The unit should be replaced immediately if it is not operating properly. The performance of smoke alarms older than 10 years is simply not reliable. To ensure your family's safety, all carbon monoxide and smoke/CO combination alarms need to be replaced every 5-7 years. All smoke alarms need to be replaced every 10 years.

If it's time to replace your alarms, consider the NEW 10-Year Life series and never have to worry about a battery replacement for the life of the alarm.10-Year alarms are available in smoke,carbon monoxide and combination alarms.

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