Hardwired Smoke Detector Cost Ontario

Most hardwired smoke detector replacements in Ontario are priced per device when the wiring and electrical box are already in place. City Power replaces expired detectors with combination smoke/CO units that have battery backup, typically $90–$150 per unit installed.

That price is for a straightforward replacement: remove the old alarm, confirm the box and wiring are suitable, install the new hardwired unit, connect the backup battery, test the alarm, and clean up. If the home needs new interconnect wiring, extra boxes, access through finished ceilings, or troubleshooting of a dead alarm circuit, the job is quoted in writing after a site visit.

For booking, see our smoke and CO detector installation service. City Power Electrical Services is a Licensed Electrical Contractor, ECRA/ESA #7015314, founded and run by Sam, a licensed electrician.

The usual cost is $90–$150 per unit when replacing existing hardwired alarms

The lowest-friction job is a like-for-like replacement of existing hardwired detectors. The electrical box is already in the ceiling, the 120V feed is present, the interconnect conductor is already there, and the locations already make sense for the home.

We replace expired detectors with combination smoke/CO units that have battery backup, typically $90–$150 per unit installed.

That normally includes:

• Supplying a hardwired combination smoke/CO alarm with battery backup
• Removing the expired or failed device
• Checking the existing electrical box and conductors at that location
• Connecting the 120V power, neutral, and interconnect lead where present
• Installing the mounting plate and alarm head
• Confirming the green power indicator, test button, and alarm response
• Cleaning up packaging and old devices from the work area

A hardwired alarm is not just a plastic disc on the ceiling. Behind it, there is usually a small junction box, a plug-in harness, a black hot conductor, a white neutral, and an interconnect conductor that lets all alarms sound together. Older alarms may have a different harness, brittle plastic, missing battery drawers, painted-over covers, or dates showing they are past their service life.

If the alarm chirps after replacement, the cause is often not the new device. Common causes include a loose neutral in the alarm box, a failed alarm elsewhere on the same interconnect loop, mixed incompatible alarm brands, or a backup battery tab that was never fully removed.

Running new detector wiring is a different job and is quoted after a site visit

Installing new hardwired alarms where none exist costs more than replacing devices because the electrician has to create the wiring path, not just change the heads.

New wiring can involve:

• Fishing cable through finished ceilings or attic spaces
• Adding electrical boxes at the correct alarm locations
• Connecting alarms together with an interconnect conductor
• Finding a suitable 120V source that is not controlled by a wall switch
• Working around insulation, vapour barrier, joists, plaster, or pot light layouts
• Repairing amateur splices or disconnected alarm loops
• Filing an ESA notification where required and arranging inspection

Because access changes the labour so much, new detector wiring is quoted in writing after a site visit. A bungalow with attic access is a very different job from a finished three-storey Toronto semi with plaster ceilings and no accessible chase.

The biggest cost divider is whether the alarms are already interconnected. If one alarm sounds and every other alarm in the home sounds, the interconnect is likely working. If only one device sounds, the interconnect may be missing, disconnected, or incompatible with the replacement devices.

We also separate detector work from unrelated electrical upgrades. If your panel is full, a junction box is buried, or a lighting circuit has ungrounded old wiring, that may need separate repair. For other small-device pricing, see our outlet installation cost guide and switch installation cost guide, but smoke and CO alarms have their own placement and interconnection requirements.

Ontario homes need smoke alarms, and many homes also need CO alarms

Ontario requires working smoke alarms in homes. The common practical standard is smoke alarms on every storey and outside sleeping areas. Many modern layouts also use alarms inside bedrooms, especially where newer construction or renovation standards apply.

Carbon monoxide alarms are required in many Ontario homes, especially where there is a fuel-burning appliance, fireplace, or attached garage. CO alarms are placed near sleeping areas so people are warned before carbon monoxide exposure becomes dangerous while they are asleep.

For rental housing, detector maintenance is not optional. Landlords must provide and maintain required alarms, and tenants must not disable them. A missing battery, disconnected alarm head, painted-over alarm, or expired device can become a compliance issue, not just a nuisance chirp.

In practical terms, we look for three things:

• Coverage: alarms in the required areas for the home layout
• Power: hardwired 120V supply with battery backup where applicable
• Interconnection: one alarm sounding causes the rest to sound where the system is designed that way

Combination smoke/CO units are often the cleanest replacement in hallways and near sleeping areas because one device handles both hazards. They still need the right location. For example, a CO alarm belongs near sleeping areas, while smoke alarm placement also has to consider stair openings, bedroom corridors, and each storey.

Kitchens, bathrooms, laundry rooms, furnaces, and garages need careful placement. Too close to steam, cooking vapour, dust, or combustion appliances, and you can get nuisance alarms. Too far from sleeping areas, and the alarm may not provide the warning it is meant to provide.

Price depends on device count, access, interconnection, and whether the old system is working

The per-unit price is straightforward when the existing hardwired system is healthy. The number changes when the wiring has to be found, repaired, extended, or brought into a usable condition.

Device count still matters, but not all devices are equal. Replacing a hallway alarm under a standard ceiling is simple. Replacing a basement alarm tied into older junctions, or adding a new alarm in a finished upper hallway with no attic access, is a wiring job.

We also check the manufacture date. Many homeowners look only at the battery, but smoke and CO alarms have a service life. If the date on the back is expired, replacing the battery does not make the sensor new again.

If you are buying or selling a home and want a broader safety review, our electrical inspection cost guide explains what a panel, grounding, GFCI, detector, and visible wiring inspection typically covers.

A proper replacement includes testing every alarm, not just swapping the plastic head

A good detector visit should end with a full test. The test button should activate the local sounder, and interconnected alarms should respond together. The battery backup should be installed and active. The alarm head should lock cleanly onto the base, and the power indicator should show the unit has 120V supply.

We also look for common failure points:

• Painted alarm covers that block the sensing chamber
• Missing backup batteries or battery drawers left open
• Hardwired alarms hanging loose from the ceiling
• Old harnesses forced into new devices
• Mixed alarm types that do not communicate properly
• Dead alarm boxes with no 120V feed
• Interconnect conductors capped off or never connected
• Basement alarms mounted too close to dusty mechanical areas
• Hallway alarms placed too close to bathroom steam

In many homes, the immediate complaint is a chirp. The cause might be an expired CO sensor, a dying backup battery, an alarm at the end of its life, or one failed device causing confusion across the whole interconnect loop. Replacing every expired unit at once is usually cleaner than changing one head today and chasing nuisance chirps from the next expired head later.

For landlords, we recommend keeping device dates, locations, and test results documented. A simple record of what was replaced, where it was installed, and when it was tested is useful for rental compliance and for future maintenance planning.

To get an accurate quote, count the devices and note what happens when one alarm is tested

The fastest way to price the job is to collect a few details before calling.

Have this ready:

• How many alarms are in the home
• Whether they are smoke-only, CO-only, or combination smoke/CO units
• Whether they are hardwired, battery-only, or a mix
• The manufacture dates printed on the backs of the alarms
• Whether one test button makes all alarms sound
• Which alarms are chirping, dead, loose, painted, or missing
• Whether ceilings are finished, open, plaster, or accessible from an attic
• Whether the property is owner-occupied, rented, or being prepared for sale

City Power provides free written estimates. For straightforward replacement, the published range is $90–$150 per unit installed for combination smoke/CO units with battery backup. If new wiring, interconnection, or troubleshooting is needed, we quote the work in writing after a site visit.

Where an ESA notification is required, we handle the permitted process and inspection. Every job is done under City Power Electrical Services, Licensed Electrical Contractor ECRA/ESA #7015314, with full cleanup at the end.

We serve Toronto and the GTA, including North York, Scarborough, Etobicoke, Mississauga, Brampton, Markham, Vaughan, Richmond Hill, Oakville, Burlington, Pickering, Ajax, Whitby, Oshawa, Hamilton, Barrie, and nearby communities. For more pricing articles, visit the City Power electrical cost guide hub, or book directly through our smoke and CO detector service page.