How to Install and Wire a Smoke Detector in a Hardwired System

Smoke Detectors

Residential building codes require smoke detectors to be in every home. And it's a good thing that they do. Fires can begin quietly and go undetected until it is too late. To prevent this from happening, these alarms are essential for keeping your family and property safe.

Smoke detectors only work when they have a continuous electrical charge, whether this is from a battery or from being hardwired into the home's electrical system. And because a fire can happen at any time, it's vital for this electrical charge to remain uninterrupted.

Oftentimes, though, smoke detectors fail due to dead batteries. While it's a best practice to change the batteries in a smoke detector every six months, having one hardwired into the home electrical system ensures you'll never be without a working smoke detector.

In this article, we'll explain what a hardwired smoke detector is and walk you through the steps electricians take to install these alarms in your home:

What Is a Hardwired Smoke Detector?

When a device or appliance is “hardwired,” it means that it's directly connected to the home's electrical circuits and is not “plugged in” to an electrical outlet or running off batteries.

While a hardwired smoke detector may look the same as a battery-powered smoke detector when it's up on your wall or ceiling, its constant electrical current limits the possibility of failure. It's important to note that in the event of a power failure (blackout), hardwired smoke detectors have a back-up battery on board to make sure it continues to work.

The addition of a battery is crucial because fires can cause electrical problems and blackouts within a home, limiting the functionality of the smoke detector if it is only powered via a wired connection.

male electrician on a ladder installing a smoke detector while female electrician writes on clipboard

How to Install a Hardwired Smoke Detector

Time Required: About 1–3 hours

Materials Needed: Stud finder, electrical wire, multimeter, smoke detector, power drill, saw, wire cutters, and screws

Step 1: Turn Off the Power

Determine which existing circuit the smoke detectors will be wired into and turn off the power supply to that circuit. Safety first! Keep in mind that any wiring tasks should be done by an electrician, as there is always a risk of shock or electrocution when carrying out this type of work.

Step 2: Cut the Holes

Use a stud finder to locate the ceiling joist or wall stud as the location for the smoke detector. The electrical box makes a great template to trace around, so the hole should be cut precisely in-between the wall studs. Using a level ensures that the outline of the box is level.

After determining the install location, drill a pilot hole in the middle of the outline for the electrical box, and then cut around the template outline. The electrical box should be a snug fit, but not too tight. If more than one smoke detector is being wired, your electrician will repeat this process for each unit.

Step 3: Run the Wire

From the power source, run wire (with ground) to the location of the smoke detector. The power source can include an existing wall outlet, wall switch, or circuit breaker panel. A good amount of excess cable will be left extending through the hole in the drywall. This ultimately makes installation easier, and your electrician will trim the wire to the proper length when installing a hardwired smoke detector.

If multiple smoke detectors are being installed, your electrician will run a 3-wire cable (with ground) from the first smoke detector to each subsequent smoke detector. The extra wire allows the smoke detectors to communicate with one another so that if one smoke detector detects smoke, all detectors will go off.

Step 4: Attach the Wires to the Electrical Boxes

At each box location, about 8 inches of wire will extend from the hole. Then, remove the insulating wrap from the wire using a cable stripper. The wires will then be run and clamped to the electrical boxes.

Step 5: Secure the Electrical Boxes

Once the cables have been secured to each box, it's time to secure the electrical box in the opening of the drywall.

At each smoke detector location, feed the circuit wires through the detector's mounting plate and align the screw holes on the mounting plate to the hole in the electrical box. Using the screws that came with the smoke detector, secure the smoke detector in place.

Step 6: Wire the Smoke Detector

The smoke detector has two parts: the alarm itself and the harness (with wires coming out of it that plug into the alarm after the wires have been connected). Connect the wiring harness with the black, white, and red wires coming through the nearest electrical box.

Step 7: Put It All Together

Once the smoke detectors have been wired, attach the mounting plate to the electrical box with screws. Then, the wire harness is attached to the back of the smoke alarm. The notches on the back of the alarm align with those on the base, and with a quick twist, the unit is ready to go.

Step 8: Connect to the Circuit

Finally, the pigtail the wires into the circuit and join the smoke detector cable to the circuit. With the wires joined, it's time to restore power to the circuit and go through the setup steps for your new hardwired smoke alarms.

Count on Mr. Electric for Smoke and Carbon Monoxide Alarm Installation

As you can tell, installing hardwired smoke detectors is a complicated process. Your friends at Mr. Electric are happy to help! We're available to install your hardwired smoke alarm and carbon monoxide alarm system for you. We would also love to discuss the option of using smart smoke detectors, to keep you connected and your home protected at all times. Give us a call at (844) 866-1367 or request an appointment online today.