Smoke and carbon monoxide detectors should be tested monthly using the test button, have their batteries replaced at least once a year, and be replaced entirely about every ten years for smoke alarms and every five to ten years for CO alarms, based on the manufacture date printed on each unit.
Where detectors belong
Placement is what makes the difference between an alarm that wakes you and one that goes off too late.
Smoke alarms go inside every bedroom, outside each separate sleeping area, and on every level of the home including the basement. Mount them on the ceiling where possible, or high on a wall within a foot of the ceiling, because smoke rises. On a vaulted ceiling, mount near the peak but not at the very apex, where air can stagnate.
Keep smoke alarms at least ten feet from cooking appliances and away from bathroom doors where steam escapes. Avoid mounting in the path of supply registers or ceiling fans, which can blow smoke away from the sensor.
Carbon monoxide alarms go outside each sleeping area and on every level. CO mixes fairly evenly with air, so height is less critical than it is with smoke — follow the manufacturer's instruction for the specific unit. Place one near the furnace and gas appliances, but not directly above or within a few feet of them, since normal startup can trigger a nuisance alarm.
Do not install either type in unconditioned attics or garages, where temperature extremes shorten sensor life.
Test and battery cadence
- Monthly: press and hold the test button on each unit until it sounds. If it is weak, slow or silent, deal with it that day.
- Yearly at minimum: replace batteries in any unit that takes a replaceable battery. Many people anchor this to the fall time change, which is a reasonable reminder.
- Immediately: replace the battery on any chirp. A single intermittent chirp is the low-battery warning, and it will always start at three in the morning.
- Every few months: vacuum the cover with a brush attachment. Dust and insects are a leading cause of nuisance alarms.
Sealed ten-year lithium units remove the battery question entirely — when the battery dies, the unit has reached its service life and gets replaced whole. For hardwired detectors with battery backup, the backup battery still needs changing on schedule, because that is what carries the unit through a power outage.
The replacement rule
Detectors do not last forever, and this is the part most households miss. The sensing element degrades whether or not the unit ever alarms, so a detector that passes its button test can still be past its useful life. The button tests the horn and circuit, not the sensor.
Take each unit down and look at the back. There is a manufacture date printed there. Smoke alarms get replaced roughly every ten years from that date. CO alarms have shorter sensor lives — typically five to ten years depending on the model, with the end-of-life date often printed on the unit.
Write the replacement year on the unit with a marker when you install it. It is the only way the information survives the decade.
Why CO matters more in heating season
Carbon monoxide comes from incomplete combustion, which means it comes from the appliances that run hardest in winter — the furnace, the water heater, a gas fireplace, a boiler. A cracked heat exchanger, a blocked or disconnected flue, a backdrafting water heater, or a furnace starved of combustion air all produce CO, and all of them are heating-season events.
Colorado adds two factors. At 6,035 feet, combustion equipment is derated for altitude and must be set up accordingly; a unit configured on sea-level assumptions burns less cleanly. And winters here mean a tightly closed house for months, so there is nowhere for CO to go.
CO is colorless and odorless. Headache, dizziness, nausea, confusion and fatigue that improve when you leave the house are the symptoms, and they are easy to mistake for flu. If a CO alarm sounds, get everyone outside into fresh air and call 911 from outside — then have the combustion appliances inspected before anyone goes back in. Smith services detectors and the heating equipment behind the alarm.
Combination units vs separate detectors
Combination smoke/CO units cover both hazards from one device, which means fewer things on the ceiling and fewer things to forget. They are a reasonable choice for most homes, especially in hallways outside bedrooms.
The trade-off is that the two sensors have different service lives, so the shorter one — usually CO — determines when you throw out a perfectly good smoke sensor. They also have to sit where both sensors work well, and the ideal spot for one is not always ideal for the other.
Separate units let you place each one optimally and replace them on their own schedules. Many homes do best with a mix: combination units in hallways, dedicated smoke alarms in bedrooms, and a CO alarm near the mechanical room.
Whatever you choose, interconnection matters more than the unit type. When detectors are interconnected, one alarm sounds them all — so a basement fire wakes someone sleeping upstairs. Hardwired interconnection is standard in newer construction; wireless interconnection is available for retrofits in older homes.
What a licensed technician does that you can't
Testing and battery changes are genuinely homeowner work. The rest is not.
A licensed electrician installs and interconnects hardwired detectors, adds detectors on a dedicated circuit where code requires it, and confirms the whole interconnected system actually triggers together rather than assuming it does. In older Colorado Springs homes with undersized panels and original wiring, that work frequently exposes other issues worth addressing.
On the CO side, a licensed HVAC technician is the only person who can find the source. They inspect the heat exchanger for cracks, test combustion with an analyzer, verify draft and venting, confirm adequate combustion air, and check that the equipment is configured for altitude. An alarm tells you CO is present; it does not tell you why, and guessing at that is not something to attempt.
If your detectors are past their dates, missing from bedrooms, or not interconnected, fixing that is one of the highest-value jobs in the house.
Frequently asked questions
How often should smoke detectors be replaced?
Replace smoke alarms about every ten years from the manufacture date printed on the back of the unit, not from the day you installed it. The sensing element degrades over time whether or not the alarm ever sounds, and the test button only confirms the horn and circuit work — it does not test the sensor itself.
Where should carbon monoxide detectors be placed in a house?
Install carbon monoxide alarms outside each separate sleeping area and on every level of the home, including the basement. Put one near the furnace and gas appliances, but not directly above or within a few feet of them, since normal startup can cause nuisance alarms. Follow the specific unit's mounting-height instructions.
Why does my smoke detector chirp at night?
An intermittent chirp is almost always the low-battery warning, and it tends to start overnight because the drop in household temperature reduces battery output slightly. Replace the battery rather than removing it. If a unit chirps with a fresh battery, check the manufacture date — it may have reached end of life and need replacing entirely.
Are combination smoke and CO detectors a good idea?
They work well for most homes and mean fewer devices to maintain, especially in hallways outside bedrooms. The trade-off is that the carbon monoxide sensor usually has a shorter life than the smoke sensor, so the whole unit gets replaced on the shorter schedule. Many homes use a mix of combination and dedicated units.