How long do smoke detectors last?

Most smoke detectors should be replaced at 10 years, even if they still beep when tested.

The test button only proves the horn, battery, and basic electronics respond. It does not prove the sensing chamber will react properly to smoke after years of dust, humidity, cooking residue, insects, paint overspray, or age-related sensor drift.

For most residential smoke alarms, the practical rule is: replace the whole alarm 10 years after the manufacture date. Do not count from the closing date of the house, the date of your renovation, or the day the battery was last changed.

Look for one of these markings on the back or side of the unit:

• Manufactured on or MFG date
• Replace by or expiry date
• A month/year stamped into the plastic label
• A QR code or model label that points to manufacturer documentation

If you cannot find a date, treat the alarm as suspect and replace it. A missing or unreadable label is common on older hardwired alarms that have been painted around, exposed to kitchen grease, or left in place through several renovations.

A useful check is to twist the detector off its mounting plate and read the back. For hardwired alarms, do not pull on the wires. The plug connector should release gently. If the alarm is brittle, painted shut, hanging loose, or connected with an odd adapter, it is time to have the detector setup reviewed rather than just snapping in another unit.

If you are replacing multiple alarms, it is often better to do them all at once. Mixing old and new units can create compatibility problems, especially with interconnected alarms where one detector is supposed to trigger the rest of the house.

Smoke alarms and CO alarms both expire, but they are not the same device.

A smoke alarm senses smoke from a fire; a carbon monoxide alarm senses CO from combustion appliances, fireplaces, attached garages, or other sources. Combination smoke/CO alarms are convenient, but each sensor still has an end of life.

The exact lifespan depends on the manufacturer and model. Many current alarms are designed around a 10-year replacement cycle, while some CO alarms have shorter service lives. Always follow the label on the device if it gives a specific replacement date.

Battery backup matters. A hardwired alarm without working backup can be silent during an outage. A battery-only alarm can be removed, disabled, or forgotten. In homes with 120V hardwired alarms, the replacement should maintain backup protection, usually with a sealed battery or replaceable battery depending on the model.

Do not assume a plug-in CO alarm in a hallway replaces required smoke alarms. Do not assume a smoke alarm in a bedroom protects against carbon monoxide. The device type, listing, placement, and expiry all matter.

For a straightforward replacement program, City Power installs current combination smoke/CO alarms with battery backup where appropriate; expired detector replacement is typically $90–$150 per unit installed. Larger upgrades, new wiring, or interconnection work are quoted in writing after a site visit. See our smoke and CO detector installation service for the practical options.

Replace the detector sooner if it is past date, contaminated, damaged, incompatible, or giving an end-of-life signal.

You should not wait for the full 10 years if the alarm has obvious problems. A detector is a life-safety device, not a decorative cover plate.

Replace the alarm now if you see any of these conditions:

• The label says it is expired or the manufacture date is more than 10 years old.
• The date label is missing, painted over, or unreadable.
• The alarm has turned yellow or brown from age, smoke, grease, or sunlight.
• The cover is cracked, loose, painted, or clogged with dust.
• It chirps after a fresh battery and reset.
• It will not sound when tested.
• It was exposed to a leak, renovation dust, sanding, drywall work, or spray paint.
• It is a recalled or discontinued model and compatible replacements are no longer available.
• A hardwired alarm has been disconnected and left hanging.

Renovation dust is a big one in GTA homes. Sanding plaster, cutting drywall, spraying texture, or doing kitchen work can load the sensing chamber. Vacuuming the outside may help with light dust, but it does not make an old alarm new again.

Paint is another clear failure mode. If a detector was painted to match a ceiling, its vents may be sealed. Replace it. A painted alarm should not be cleaned and reused.

A repeating chirp is not always an expiry signal; it can be a low battery, loose battery door, dirty chamber, wiring issue, or end-of-life alert. If your concern is active beeping or nuisance alarms, read why a smoke alarm goes off. If the issue is an indicator light rather than age, see why a smoke detector flashes red.

In Ontario homes, placement and interconnection matter as much as age.

A current, working detector in the wrong place is not enough. Ontario requirements depend on the building type, age, layout, fuel-burning equipment, attached garage, rental use, and renovation scope. In general, homes need working smoke alarms on every storey and near sleeping areas, and CO alarms are required in specific locations where carbon monoxide risk exists. Confirm exact placement with the current Ontario Fire Code, your municipality, or the authority having jurisdiction if the home is unusual.

Common detector layouts we review include:

• One alarm outside bedroom areas, but no alarm on another storey.
• Basement smoke alarms missing after a finished basement renovation.
• CO alarms installed too far from sleeping areas.
• Old 120V smoke alarms that are hardwired but not interconnected.
• Additions where the new area has modern alarms but the older house does not.
• Rental or secondary-suite layouts that need a more careful alarm plan.

Interconnection is important because a basement fire may not wake someone sleeping upstairs quickly enough if only the basement alarm sounds. With interconnected alarms, one triggered device sounds the others.

Hardwired interconnection can be done with a 120V feed, neutral, and an interconnect conductor between alarms. Some approved systems use wireless interconnection where running a new interconnect wire is impractical. The right choice depends on ceiling access, attic or basement access, existing wiring, and whether the detectors are part of a renovation.

If you are deciding whether to keep battery-only alarms or upgrade the system, read should I hardwire smoke detectors?. For many homes, the best time to upgrade is during a basement finish, rewire, panel work, or ceiling renovation, because the walls and ceilings are already being opened.

Hardwired upgrades should be planned, permitted where required, and tested as a whole system.

If new 120V wiring, new detector locations, or interconnection wiring is being added, it should be handled as electrical work, not as a handyman swap. Where ESA notification is required, the electrical contractor should file it and arrange inspection.

A proper detector upgrade is not just “put one on the ceiling.” The electrician should confirm:

• The detector locations match the house layout and sleeping areas.
• Smoke and CO functions are used where needed.
• The alarm type is compatible across the interconnected group.
• The circuit supply is reliable and not controlled by a wall switch.
• Battery backup is present and accessible or sealed as designed.
• The interconnect conductor or wireless link triggers all required alarms.
• Devices are not too close to vents, ceiling fans, bathrooms, or cooking areas where nuisance alarms are likely.
• The homeowner knows the test, silence, battery, and expiry procedures.

For simple expiry replacement, the work may be quick: remove the old alarm, confirm the wiring and mounting, install a compatible replacement, test the horn, and label the date. For a full-house hardwired upgrade, access is the real variable. An unfinished basement ceiling, attic access, or an open renovation makes the job much cleaner than fishing wires through finished plaster.

Costs depend on whether the job is like-for-like replacement or new wiring. For replacement of expired combination smoke/CO units with battery backup, expect $90–$150 per unit installed. If the house needs new hardwired locations, interconnection, ceiling fishing, or circuit changes, the work is quoted in writing after a site visit. For a fuller cost discussion, see how much smoke detector installation costs.

City Power Electrical Services is a licensed Ontario electrical contractor, ECRA/ESA #7015314, and we file ESA notifications where required for detector wiring upgrades in Toronto and the GTA.

The safest rule is simple: if the alarm is 10 years old, undated, contaminated, not interconnected where it should be, or missing battery backup, replace it before you need it.