How to Test Your Smoke and Carbon Monoxide Alarms

Why this matters

A smoke or carbon monoxide alarm looks exactly the same on the ceiling whether it works or not. The only way to find out is to make it sound, and most alarm makers ask you to do that at least once a month. The test takes about ten minutes for a whole house. Done properly it also tells you three things the button alone cannot: whether the alarms are talking to each other, whether any of them have aged out, and whether the batteries are current. This card walks the monthly test, then shows one house's results written up so you can see what a finding looks like.

Step 1: Warn the household, and the monitoring company if you have one

Tell everyone at home that the alarms are about to sound and that it is a test. If anyone in the house is hard of hearing, sensitive to noise or likely to be frightened, tell them first, and put pets in a room away from the nearest alarm.

If your alarms are connected to a monitored security system, call the monitoring company before you start and ask them to put your system on test. Call them again when you finish to take it off test.

Why: an alarm test that nobody expected is how a household learns to ignore the sound, and an alarm test on a monitored system that nobody told the monitoring company about can send the fire department to your door. The test should never set off a real emergency response.

Step 2: Reach the button safely

Use a sturdy step stool or ladder with someone nearby, rather than a chair. Many alarm makers say you can press the test button with the end of a broom handle from the floor instead; check your alarm's instructions. The horn is loud at close range, so cover the ear nearest the alarm.

Step 3: Press and hold the test button until it sounds

Press the button and hold it. Some alarms sound within a second; others take several seconds of holding. Listen for the pattern:

• Smoke alarms: three beeps, a pause, three beeps, repeating.
• CO alarms: four beeps, a pause, four beeps.
• Combination alarms usually sound both patterns in turn, and many add a spoken message naming smoke or carbon monoxide.

Release the button and it should go quiet within a few seconds.

What breaks if you skip the hold: a quick tap that produces nothing gets mistaken for a dead alarm, and a working alarm comes down. If a firm press held for several seconds produces nothing, then it has failed: replace the battery if it has one and test again, and if it still does not sound, replace the alarm.

Step 4: Confirm the interconnected alarms all sound

Many houses have interconnected alarms: when one senses smoke, all of them sound. They are linked either by a wire in the walls (alarms that are wired into the house electrical system, with a battery for backup) or wirelessly. If yours are linked, pressing test on one should set off every one.

Have helpers stand in the bedrooms and the basement, or walk the house yourself while one alarm is sounding. Then press test on each of the other linked alarms in turn and check again each time: an alarm can receive the signal but fail to send it, and that only shows when its own button is the one pressed.

Why: interconnection is what wakes a sleeping child in a far bedroom when the fire starts in the basement. An alarm that sounds on its own test but stays silent when another is tested has lost its link, and nothing else in the monthly routine catches that.

If one stays silent: for alarms wired into the house, call an electrician, since the link runs through house wiring. For wireless alarms, the manual explains how to re-link them.

Step 5: Read the date on every alarm

Each alarm has a manufacture date printed on its back or side; you usually have to twist it off its base to see it. Many also print a "replace by" date.

• Smoke alarms are replaced 10 years after the date they were made, per NFPA 72, the national fire alarm standard, in the edition your jurisdiction has adopted, and per the alarm makers. Not 10 years after you installed it.
• CO alarms are replaced on the maker's schedule, commonly somewhere between 7 and 10 years. Many sound an end-of-life chirp or signal when they reach it. The label says which.

Write the date somewhere you can see it from the floor, such as on the base edge, so next month you do not have to take it down again.

Step 6: Replace the batteries where the alarm uses them

• Alarms with replaceable batteries, including the backup battery in a wired-in alarm: replace on the schedule in the alarm's manual, commonly once a year, and any time it chirps for low battery.
• Sealed 10-year alarms: there is no battery to change. When one reaches its end of life, the whole alarm is replaced.

Use the battery type printed on the alarm.

Step 7: Write it down

Date, time, each alarm, whether it sounded on its own test, whether it sounded when another was tested, its manufacture date, and any battery changed. Your records file is where this goes. See related: Your House Records File and What Goes In It.

What the test button checks, and what it does not

On most alarms the test button checks the battery or power supply, the electronics and the horn. That is worth knowing every month. It does not prove that smoke can still get into the sensing chamber, which dust, cobwebs, paint and cooking grease can block, and it does not prove that a CO sensor is still accurate. Sensors age, which is why the replacement dates exist at all: an old alarm can pass its button test every month and still be slower than it should be to sense a real fire.

So the date in Step 5 matters as much as the beep in Step 3. Never test an alarm with an open flame, a candle or burning paper. Some alarms allow an aerosol test product made for the purpose; use one only if your alarm's instructions say so. Clean the alarm's vents the way its manual describes, usually with a vacuum brush, and never paint over one.

One house's October test, written up

The house: two stories and a basement. Seven alarms: one combination smoke and CO alarm in the upstairs hall, a smoke alarm in each of three bedrooms, a smoke alarm in the main floor hall and one in the basement, all six wired in and interconnected with 9-volt backup batteries except the combination alarm, which has a sealed battery. A separate battery-only CO alarm sits on the basement wall near the furnace and is not linked to the others. No monitoring company. October is the month this household changes the batteries.

ALARM TEST LOG          2026-10-18, 10:05 a.m.
household warned: yes   monitoring company: none

#  where         type  made     own  linked  battery
1  upstairs hall S+CO  2021-03  ok   ok      sealed
2  bedroom 1     S     2014-06  ok   ok      new 9V
3  bedroom 2     S     2019-09  ok   SILENT  new 9V
4  bedroom 3     S     2019-09  ok   ok      new 9V
5  main hall     S     2019-09  ok   ok      new 9V
6  basement      S     2019-09  ok   ok      new 9V
7  basement      CO    2017-01  ok   n/a     new AAs

own    = sounded on its own test button
linked = sounded when each other linked alarm
         was tested, and set the others off

What the log says, alarm by alarm:

• Every alarm sounded on its own button, so all seven have working horns and power.
• Number 2 was made in June 2014. In October 2026 that is 12 years and 4 months old, past the 10-year limit. It passed its test and is replaced anyway, because the sensor's age is the reason for the limit.
• Number 3 sounded on its own but stayed silent whenever another alarm was tested, and testing 3 did not set off the others either. Its link is broken, so the bedroom 2 child would not hear an alarm that started in the basement. That is an electrician call, and the household notes it on the log with the date they booked it.
• Number 7 was made in January 2017, 9 years and 9 months ago. Its label gives a 10-year life, so it is still in service but due by January 2027. They write "replace by 01/2027" on its face and put a reminder in their calendar.
• Numbers 1 and 7 are the only CO alarms in the house, and number 7 sounds only in the basement. That is worth raising with whoever replaces number 2, since where CO alarms go is its own question. See related: What Your Carbon Monoxide Alarm Is Telling You.

What would have changed the morning:

• A monitored system would have meant a call to the monitoring company before the first button was pressed and another after the last.
• Sealed 10-year alarms throughout would have removed the battery column entirely and left the date column as the one that matters most.

When an alarm is due for replacement

Replace an alarm when any of these is true: it is past 10 years from manufacture (smoke) or past the maker's stated life (CO); it gives an end-of-life signal; it does not sound on a firm, held test press after a fresh battery; it has been painted over or damaged; or the maker's instructions say to replace it after it sensed a real CO event. Battery-only alarms you can replace yourself, matching the type and following the instructions. Alarms wired into the house involve house wiring; many households have an electrician do it, and an electrician is the call when the link between alarms is the problem.

See related: What Your Smoke Alarms Need From You, for where alarms belong and what their chirps mean.

References

• NFPA 72, National Fire Alarm and Signaling Code, in the edition your jurisdiction has adopted: household alarm testing, the 10-year smoke alarm replacement rule, and the three-beep and four-beep alarm patterns (CO alarm provisions sat in NFPA 720 before NFPA 72 absorbed them in its 2022 edition, so an older adopted edition points there)
• Your alarms' manufacturer instructions, which set the test method, battery schedule and CO alarm service life
• See related: What Your Smoke Alarms Need From You
• See related: What Your Carbon Monoxide Alarm Is Telling You
• See related: How to Respond When Your Carbon Monoxide Alarm Goes Off