Smoke Detector and Carbon Monoxide Alarm: When to Replace

Most homeowners know to test smoke detectors and replace batteries. Fewer know that detectors have an expiration date - and that an expired detector provides false security. Here's what you need to know about maintenance and replacement.

Smoke Detector Lifespan

Replace smoke detectors every 10 years.

The sensors in smoke detectors degrade over time and become less sensitive. A 12-year-old detector may appear to work (it passes the battery test) while being significantly less responsive to actual smoke.

The manufacture date is printed on the back of every smoke detector. If you don't know how old your detectors are, check the date on the back. Many homeowners discover detectors that are 15-20 years old.

Carbon Monoxide Alarm Lifespan

Replace CO detectors every 5-7 years (depending on the manufacturer - check the label).

CO alarms use electrochemical sensors that degrade faster than smoke alarm technology. A CO detector older than 7 years should be considered unreliable even if it tests as functional.

Note: combination smoke/CO alarms follow the CO sensor's shorter lifespan - replace the whole unit when the CO sensor expires, even if the smoke sensor is still within its 10-year window.

California-Specific Requirements

California law requires: - Smoke detectors: On every floor, inside each bedroom, outside each sleeping area. Battery backup required for hardwired units. - CO alarms: Required in all homes with a fossil fuel burning heater, attached garage, or fireplace. Required in each bedroom or within 15 feet of each sleeping area.

If you're selling a home in California, smoke and CO detectors must be in place and working as a condition of sale.

Battery vs. Hardwired Detectors

Battery-only: Simpler, easier to install anywhere. Modern 10-year sealed lithium battery detectors eliminate the low-battery chirp problem (the battery lasts the life of the detector).

Hardwired: Connected to your home's electrical system with a battery backup. Required in many California new construction installations. More reliable during extended outages (battery backup keeps them running). Installation requires a licensed electrician if new wiring is needed.

Interconnected: When one alarm sounds, all alarms in the network sound. This is the safest configuration for two-story homes or homes where you might not hear an alarm in a remote part of the house. Available in both hardwired (interconnected through wiring) and wireless (RF interconnected) configurations.

When to Test

Test all smoke and CO detectors monthly by pressing and holding the test button until the alarm sounds. If it doesn't sound, replace the battery first. If a new battery doesn't fix it, replace the unit.

Annual tasks: - Replace batteries in battery-powered detectors (unless sealed 10-year battery) - Vacuum around the detector to remove dust that can accumulate on sensors - Check the manufacture date and note which units are approaching replacement age

Where to Place Detectors

Smoke detectors: - Inside each bedroom - Outside each sleeping area (hallway between bedrooms) - On each floor of the home including basement - At least 10 feet from cooking appliances to minimize false alarms

CO detectors: - In or near each sleeping area - Near any fossil fuel appliance (furnace, water heater) - but not directly above (CO drifts first, check manufacturer placement guidance) - One on each floor

Not on the ceiling directly next to: - Kitchen range (false alarms from cooking) - Bathroom (humidity affects sensors) - Ceiling corners and dead air spaces

Common Problems and Fixes

Chirping without alarm: Low battery in a battery-powered unit. Replace the battery. If chirping continues with a new battery, the unit is at end of life - replace it.

False alarms from cooking: Move the kitchen detector at least 10 feet from the range. Many codes allow placement in the next room rather than the kitchen itself.

CO alarm going off without obvious source: Take it seriously. Evacuate and call 911. Common sources: attached garage with running vehicle, malfunctioning furnace, blocked flue. Don't assume it's a false alarm without investigation.

Replacing Detectors Yourself

Battery-powered detectors: Simply buy the new unit and swap it. No professional needed.

Hardwired detectors: Usually a simple plug connector that disconnects from the old unit and connects to the new. Most hardwired detectors from the same brand are backward compatible. If you're uncertain, any electrician can swap them in minutes.

Bottom Line

Smoke detectors last 10 years; CO alarms last 5-7 years. Check the manufacture date on every detector in your home. Replace expired units - old detectors that appear to work may be significantly less sensitive than they should be.

Sources and editorial notes

Prices and permit requirements vary by location, property, equipment, and scope. Treat price ranges as planning estimates and confirm current requirements with the relevant authority and contractor.

• California Contractors State License Board - when a contractor license is required
• US Department of Energy - Energy Saver
• US Consumer Product Safety Commission - home safety

Related guides

• What to Do After a Power Outage (Home Safety Checklist)
• When to Repair vs. Replace a Water Heater
• Outlet Sparking: What to Turn Off and When to Leave the House

Next step

Need professional help? Describe the job with Aniva and connect with local service providers.