Project Guide

How To Install a Smoke Detector

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Location & Placement Tips
  • When learning how to install a smoke detector, it’s important that they be installed in the proper locations in your home.
  • Don’t place smoke detectors over stoves, ovens, clothes dryers or in areas where there is the potential for significant heat or steam generation. 
  • Also check with local codes for the number of alarms required for your home and their placement.

Choosing the right room:

  • You can purchase smoke alarms that are specifically designed for different areas of your home. Most are battery-operated smoke detectors
  • Bedroom alarms feature a 10-year lithium ion battery, so you’ll never be awakened by a low-battery chirping sound in the middle of the night. Some units also feature a voice alarm to help raise you from your sleep.
  • Kitchen-specific alarms can detect both smoke and carbon monoxide, detect real fires faster and trigger fewer nuisance alarms.

Choosing the right placement:

  • Smoke rises, so the ideal location for a detector is on the ceiling. Mounting it in the center of the ceiling is best. If it needs to be mounted elsewhere on the ceiling, it must be at least 4-inches from a wall.
  • Avoid corners where the walls meet the ceiling and where pockets of dead air sometimes form, preventing rising smoke from reaching the detector.
  • Wall-mounted detectors must be installed at least 4-inches from the ceiling to avoid this dead air zone.
  • If you have vaulted ceilings, dead air can also form at the apex. Install the alarm at least 4-inches from the peak.
Installing Smoke Detectors

Most smoke alarms come with a mounting base that separates from the alarm itself. This base will have key-shaped screw holes to allow you to fasten the base to a wall or ceiling. It's time to start on how to install a smoke detector once you’ve determined the location for your alarm.

  • Select a drill bit slightly smaller than the size of the supplied wall anchors to ensure a snug fit.
  • Use the mounting base to mark the screw holes on the ceiling or wall and drill holes where marked.
  • Tap the plastic screw anchors provided into the drilled holes with a hammer.
  • Drive the supplied screws partially into the ceiling or wall and line up the mounting base with these screws.
  • Place and twist the smoke detector into position under the screws, tighten with a screwdriver and mount the smoke alarm onto the base.

Types of smoke detectors include:

  • Hardwired smoke detectors are powered directly to an AC electrical circuit, which is standard in new construction. Many also include a battery backup system to keep it functioning during power outages. One benefit of most smoke detectors is that they include a hush feature, which temporarily silences the smoke detector's alarm. 
  • Battery smoke detectors are standalone and don’t require electrical wiring. They can use a nine volt or AA battery, which should be changed twice per year. Models with lithium batteries can last up to 10 years.
  • Plug-in CO alarms plug directly into an electrical wall outlet. The plug-in design isn’t practical for smoke alarms.
Installing Hardwired Smoke Alarms
Connecting wires to the smoke detector.

A hard-wired smoke alarm or carbon monoxide alarm is connected to other detectors throughout your home. These alarms sound simultaneously, on all levels of your home, when a single unit detects smoke or gas. All the units are wired to a 120-volt household electrical circuit and each have a battery backup. The battery backup provides extra protection by powering the alarm even if a fire causes the household power to go out. It's important to learn how to install a wired smoke detector yourself.

Cut Holes for Remodeling Boxes
Person cutting hole in ceiling.

To prepare the wiring for an alarm in a new location, you need to install a remodeling box. A remodeling box is an electrical box that can be installed into drywall. This is one of the first steps to learn how to wire a smoke detector.

  • Identify where the smoke alarm will be installed. This can either be on the ceiling or on the wall 12-inches down from the ceiling.  
  • Use a stud finder to determine the location of wall studs around each alarm location.  
  • Use a marking tool to trace the outline of the wall remodeling box or ceiling remodeling box. Use a level to make sure the box outline is straight.  
  • Drill a 1/2-inch starter hole at the corner of your outline.  
  • Starting at the hole, cut along the outline with your drywall saw.  
  • Test-fit the remodeling box. It should fit into the hole snuggly, but not so tightly that you have to force it. Do not set the remodel box yet.  
  • Repeat this process at each location where an alarm will be installed. 
Run Cable to All Boxes
Detector cables hanging from the ceiling.
  • Run 14-2 NM cable (a sheathed cable with 2 wires and a ground wire) from the breaker panel to the location of the smoke alarm closest to the breaker panel. Do not connect the cable to the breaker panel yet. You’ll do this at the end of the project.  
  • When the cable reaches the alarm location, pull about 10-inches of the cable through the knockout of the first remodeling box. 
  • Run cable from the first knockout to the second knockout, leaving 10-inches of cable hanging out of the work box. Repeat this step until all remodeling box knockouts are connected by cable. 
Secure Cables and Set Boxes
Person securing the cables using a power tool.
  • Use wire strippers to strip the sheathing off the NM cable to expose the inner wires. 
  • Insert the wires through the back of the remodeling box. 
  • Insert the box into the hole in the drywall. 
  • Screw down the clamping tabs carefully until the box is tight against the wall. 
  • Attach the copper wires (ground wires) to the box with a ground screw or with the box’s internal clamp, depending on the model.  
Prepare Wires
Person using tools to prepare the wires.
  • Use wire strippers to strip 3/4-inch of insulation from the ends of the wires. 
  • Connect the wires to a 120-volt wire harness. Usually the hard-wire smoke alarm comes with a quick connect wire harness.
  • When connecting the wire harness, use wire nuts to connect the stripped NM cable wires to the same color harness wires. White wires connect to the harness’s white wire and red wires connect to the harness’s red wires. 
  • Only connect wires of like colors. 
  • When connecting smoke alarms to each other, the wire harness should connect to both the wires that run from the breaker panel (power source) and the wires that run between both alarms. 
  • Wrap the wire connectors with electrical tape for extra protection.  
  • Gently tuck the excess wire length and wire connectors into the remodeling box. Leave the plug-end of the wire harness out. 
Install Mounting Plates
Person installing the mounting plate.
  • Feed the wire harness through the smoke alarm mounting plate.  
  • Place the alarm’s mounting plate on the remodel box and align the screw holes. Make sure the wire connection runs through the mounting plate.  
  • Use the included screws to connect the mounting plate to the remodeling box.  
Connect Detector & Install Backup Battery
Person inserting the battery.
  • Plug the wire harness into the back of the smoke alarm.
  • Open the battery compartment on the alarm.  
  • Insert the correct type of battery (usually a 9-volt battery), being careful to position it so positive contact meets positive contact and negative contact meets negative.  
  • Close the battery compartment.  
Attach Smoke Detector to Mounting Plate
Person attaching the detector pieces.
  • Line up the notches on the back of the alarm with those on the base.  
  • Twist the alarm until it locks into place.  
  • Check the connection to ensure it is secure on all sides. Once secured, you've successfully learned how to replace a smoke detector.
Connect to Power Source
Person connecting wiring.
  • Connect the NM cable to the beaker panel following the step-by-step instructions in our Adding a New Circuit project guide. 
  • Alternatively, hire an experienced electrician to complete this final step for you. 

Safety Note: Always turn off the power at the breaker panel before doing any electrical work. Use a circuit tester to ensure power is off. 

Test Smoke Detectors
Person testing the smoke alarm.
  • Once all the wiring is connected at the breaker panel and no one is doing any more electrical work, turn on the power to the circuit.  
  • Confirm each alarm’s power light is on.  
  • Press the test button on each alarm. You should be able to hear all the alarms each test.  
  • If the alarms don’t sound, turn off the power at the breaker panel and double-check your wiring connections. If the connections are correct but a unit’s power light won’t come on, replace the unit. 

Hard-wired smoke detectors and carbon monoxide alarms are a necessary safety measure every home should have. Properly installing smoke detectors is an important step toward keeping you, your family and your home safe. If you have questions or are uncertain about any part of installing hard-wired smoke alarms, contact a certified electrician.  

Maintain Smoke Detectors
  • Test your smoke alarms at least once a month. On most units, this only requires the push of a button to test that the alarm sounds and the batteries are still working.
  • Change the batteries twice a year, even if you’re not hearing warning beeps. If you have a lithium ion battery model, change the batteries every 10 years or so.
  • Clean each alarm with a vacuum once a year to remove any dust or particles that may have accumulated in the unit.
  • Check the manufacture date on each unit periodically and replace them once they reach their expiration date.

If you're looking for certain items for your home, The Home Depot delivers online orders when and where you need them. For a carbon monoxide detector installation, see our How To Install a Carbon Monoxide Detector project guide

Learn more about fire safety and the steps to take to protect yourself in case of a fire.