How Often Should You Replace Smoke and Carbon Monoxide Detector? Signs Yours Are Overdue

Replace smoke detectors every 10 years, and replace carbon monoxide (CO) detectors every 5 to 7 years, or by the end-of-life date printed on the alarm (some newer CO alarms last 10 years). Test every alarm once a month. If an alarm keeps chirping after a fresh battery, or you can’t find a date on it, replace it now. 

October is Fire Prevention Month, and heating season is starting. It’s the perfect time to check the date on every alarm in your home. 

Symptoms: Signs Your Detector Needs to Be Replaced 

• Smoke and CO alarms don’t last forever. The sensors inside slowly lose their ability to detect danger, even when the test button still makes noise. Watch for these signs: 
• The date on the back is 10 or more years old (smoke) or past the printed end-of-life date (CO). 
• There’s no date at all. Older alarms often skipped it. No date usually means it’s well past due. 
• It chirps even after you change the battery. Many alarms give an “end-of-life” chirp when they’re worn out. 
• It sounds for no reason (nuisance alarms) or doesn’t sound when you press the test button. 
• The plastic has turned yellow. Yellowing is a sign of age and long exposure to heat and dust. 
• Your hardwired alarms aren’t talking to each other. If one sounds but the others stay quiet, the interconnect (the wire or signal that links them) may have failed. 

Causes: Why Detectors Wear Out 

Sensors age 

Most smoke alarms use an ionization sensor, a photoelectric (light-based) sensor, or both. Over about 10 years, dust, bugs, humidity, and normal aging make these sensors less sensitive. The alarm may still beep on test but react too slowly to a real fire. 

CO sensors have a shorter life 

Carbon monoxide is a gas you can’t see or smell. CO alarms use a chemical sensor that gets used up over time. That’s why most CO alarms need to be replaced sooner than smoke alarms. Many now have a built-in timer that chirps or shows “End” when the sensor is done. 

Power and wiring problems 

Hardwired alarms run on your home’s electrical power, with a backup battery. Loose connections, an old wiring harness (the plug-in connector behind the alarm), or a tripped circuit can leave an alarm running on battery alone without you knowing. 

Heat, dust, and placement 

Alarms near kitchens, bathrooms, garages, or attic spaces deal with steam, grease, and big temperature swings. These conditions can cause false alarms and shorten the alarm’s life. 

DIY vs. Pro 

What you can do yourself 

Press the test button on every alarm once a month. 

Replace batteries in battery-only alarms at least once a year. Many people do it when the clocks change in the fall. 

Gently vacuum the outside vents of each alarm to clear dust. 

Check the manufacture date on the back and write the replace-by year on the alarm with a marker. 

Swap out a battery-only alarm that simply screws onto a ceiling plate. 

When to call a licensed electrician 

• Hardwired alarms. These are connected to a live electrical circuit. Replacing them safely means matching the connector, confirming the circuit is safe to work on, and testing the interconnect afterward. 
• Alarms that won’t stop chirping or going off even after a battery change. 
• Adding alarms to bedrooms, hallways, or a finished basement, or upgrading to combination smoke/CO units. 
• Mixed brands or ages. Hardwired alarms from different brands often won’t link to each other, so the whole system may need to be updated together. 
• Any time a CO alarm goes off. Get everyone outside right away and call 911 or your gas utility from outside. After the all-clear, have a professional find the source. 

Technician tip: “If your smoke alarm chirps at 2 or 3 in the morning, it’s usually not haunted. Batteries lose a little voltage when the house cools down overnight, so a weak battery hits the low-battery level right when you’re asleep. Change the battery first. If the chirp keeps coming back, check the date on the alarm. And with interconnected alarms, look for the one with a flashing or solid red light. That’s usually the one that started it.” 

Seasonal Considerations 

In areas with hot summers and cold winters, fall is the best time to check your alarms. Here’s why: 

• Heating season means more CO risk. Furnaces, water heaters, fireplaces, and gas stoves all run more in cold weather. Homes are also sealed up tighter, so CO can build up faster. 
• Holiday season means more fire risk. Candles, cooking, space heaters, and decorative lights all add up from late fall through New Year’s. 
• Daylight saving time ends in early November. It’s an easy reminder to test alarms and change batteries. 
• Summer humidity and attic heat can trigger nuisance alarms near bathrooms and upper floors. If an alarm only acts up in summer, it may be in a poor spot or near the end of its life. 

Pair your alarm check with your Furnace Life Analysis so your heating system and your safety alarms are both ready before the first cold snap. 

FAQ 

How often should I replace smoke detectors? 

Every 10 years from the date of manufacture printed on the alarm, not from the day you installed it. 

How long do carbon monoxide detectors last? 

Most last 5 to 7 years. Some newer models last 10 years. Follow the end-of-life date printed on your alarm. 

Should I replace all my smoke detectors at the same time? 

Usually, yes. If they were installed together, they’re the same age. Hardwired alarms also link best when they’re the same brand and model. 

Can I replace a hardwired smoke detector with a battery-only one? 

It’s not recommended. Hardwired, interconnected alarms warn the whole home at once, and many building codes require them in homes that already have them. An electrician can replace them with matching hardwired units. 

Do combination smoke and CO alarms work as well as separate ones? 

Yes, as long as they’re listed by a testing lab like UL and placed correctly. Keep in mind the whole unit must be replaced when the CO sensor expires, which can be sooner than 10 years. 

Call Golden Rule for Smoke and CO Detector Replacement 

Not sure how old your alarms are? Our licensed electricians at Golden Rule Plumbing, Heating, Cooling & Electric can check every smoke and carbon monoxide detector in your home, replace worn-out or hardwired units, and test that they all work together. It’s one visit for real peace of mind before heating season. Call Golden Rule or book online today.