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Manuals

Photoelectric and Ionization Smoke Alarm w/ Battery Backup

The First Alert Hardwired Dual Photoelectric and Ionization Sensor Smoke Alarm with Battery Backup is designed to provide peace of mind. The photoelectric and ionization sensors on this fire detector alert you to both smoldering and fast-flaming fires, offering comprehensive detection and early warning. The 85-decibel fire alarm can connect to other compatible hardwired detectors for larger spaces.

Dual Sensors Detect Two Kinds of Fire

The First Alert Dual Sensor Smoke Alarm features photoelectric and ionization sensors for increased detection. The photoelectric sensor detects smoldering fires from objects like cigarettes burning on furniture or in trash cans, while the ionization sensor detects fast-flaming fires like erupting kitchen grease fires or combustibles. The dual sensors on this fire detector provide you and your family with the earliest warning possible.

Designed for Fewer False Alarms

Smoke from cooking or even shower steam can sometimes set off a smoke alarm. The photoelectric sensor on the First Alert Dual Sensor Smoke Alarm is sensitive to smoldering fires while reducing false alarms. The photoelectric sensor is smart enough to distinguish real threats from everyday activities, resulting in fewer annoying false alarms.

Battery Backup for Detection in a Power Outage

The fire detector is hardwired, but it also features a battery backup to help ensure the smoke alarm can still function in the event of a power outage. The unit requires two AA batteries, and comes with a low-power indicator to alert you when they need to be replaced. A one-touch silence/test button makes it easy to test the detector monthly or silence it during a false alarm.

Optipath 360° and Interconnectivity for Larger Spaces

The First Alert Dual Sensor Smoke Alarm easily connects to other compatible hardwired alarms, making it the perfect solution for larger buildings such as institutions, dormitories, hotels and other multi-family dwellings that use single station smoke detectors. The smoke and fire detector includes patented Optipath 360° technology that provides 360° of access to the alarm, and its 85-decibel siren is designed to be loud enough to awaken even the soundest of sleepers.

First Alert Hardwired Photoelectric and Ionization Smoke Alarm 3120B

How to Install First Alert 3120B Hardwired Smoke 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
(hot)
Attach to black wire on power connector
White wire
(neutral)
Attach to white wire on power connector
Orange wire
(interconnect)

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.

What is the proper placement of smoke alarms?
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.
My smoke alarm keeps chirping and beeping. Why does my smoke alarm chirp intermittently?
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.

Why doesn't my smoke alarm sound when I push the test button?
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.
Why does my smoke alarm go off when I install a battery or turn on the AC power?
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.
My smoke alarm keeps chirping, even with a new battery. What is causing this?
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.
I lost my First Alert smoke alarm owner's manual. How can I get a new one?
First Alert smoke alarm owner's manuals are available online for download at no cost. Find your alarm in our Smoke Alarms section.
Why does the National Fire Protection Association (NFPA) recommend that home smoke alarms be replaced after 10 years?
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.

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
UPC:
029054007100
MPN:
3120B
Category:
Smoke Alarms and Smoke Detectors
Product Manuals

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29 Customer Reviews

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First Alert 120VAC Hardwired Dual Sensor Smoke Alarm with Battery Backup Reviews
michael b
November 9, 2022
Verified Purchase
smoke detector

easy to install especially if you already have the newer bases installed-also like the AA cells replacing the older 9 volt

Isabel M T
October 26, 2022
Verified Purchase
Easy To Install

Installed all 4 of them and interconnected them, one in each bedroom and the basement.

Miguel Henry
December 28, 2020
Verified Purchase
Great features!

I purchased this model because of the dual smoke detection features plus the carbon monoxide and I am happy so far with the product.

Massimo Ferraris
July 1, 2020
Verified Purchase

Very Good

Philip Davis
September 11, 2019
Verified Purchase
As expected

Desired item delivered correctly as expected. Easy to install

Neil Fitzpatrick
April 20, 2019
Verified Purchase
Smoke Alarm

I received three smoke alarms. Two for replacement and one for a new installation. I have not installed them yet.

Joseph Cudzynowski
January 26, 2019
Verified Purchase
Good Product

Worked well during a recent furnace meltdown.

Anne L Haun Rymski
December 3, 2018
Verified Purchase
wired in dual smoke alarm

Son-in-law had no difficulty with installation. No false alarms which was major problem with original from another company to point it had to be disconnected.

Michael Wentink
September 20, 2018
Verified Purchase
First Alert Great products

I have just recently replaced all my smoke detectors throughout our 10 room B&B. I bought all First Alert units and particularly like the 2 AA battery design rather than the 9 volt. The batteries are much cheaper. I also later bought three wireless for each floor to improve fire alter status.

Bonnie Scherer
May 28, 2018
Verified Purchase

Item received in good shape. Easy to install. Good instructions. Product works great.

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